"But just out of curiosity, how many people on this board can say that they have had a memorable encounter with a Dragon? Specifically, that was memorable for more than just having been an encounter with a Dragon?"
In my current campaign, there is a Woodwrack Dragon (Creature Collection Revised) who has become one of the more memorable and influential NPCs of the entire campaign. My players have had a lot of fun interacting with him...but it's mostly because he's a little...unusual, as far as dragons go. Ironically enough, (considering Lord Zardoz started this thread), the Dragon's name is Zardozan, which I came up with on the fly. I thought to myself, what's the most horrible thing I've ever seen? And the answer was the movie title "Zardoz", to which I added a suffix. While Zardozan is for all intents and purposes a dragon, his body is made primarily of decomposing plant and animal matter. Moreover, he was not originally born a dragon, but instead was the result of a mad spellcaster's attempt to "ascend" to Dragonhood using an ancient artifact held within a ruined yuan-ti temple. In the course of the campaign, the PCs ventured into said temple, cleared it's inhabitants, and moved many of their allies into it as a base of operations. Shortly thereafter, they figured out how to operate the "Evolution Engine" within it, and used it to modify a creature (templates, race changes, character re-builds, or Evolved/Paragon levels are all possible with it, in theory).
One day, upon returning to the temple after a short foray into the wilds, the PCs were set upon by Zardozan, whose surprise-round breath weapon and first round of attacks left the party reeling. They were even more surprised when, after finishing his full attack, he hopped comically "back into his square" and asked "Well, had enough?!" After a bit of diplomacy, the party quickly realized that the Dragon had "rationalized" that no adventuring party would talk first, so he figured he'd get the messy combat out of the way before talking to them, which was his goal.
Essentially, when Zardozan used the temple's magic to transform himself, he'd been aiming to become a green dragon, but something had gone wrong. As a result, his current form is horribly misshapen, and he is unable to venture inside the temple to retry the experiment because of his great size (the actual focus of the Evolution Engine is on the roof, but the means of activating it is deep within the structure, and Zardozan can't risk damaging the building for fear of damaging the magic item integrated into the structure). Moreover, the transformation has left Zardozan mentally disturbed. He's brilliantly intelligent, quite charismatic, but absolutely mad as a hatter. His obsession with using the Evolution Engine again to "fix" his imperfect form is the only thing that gives him any sort of mental clarity or awareness of the outside world. The end result is a Dragon who's something of a fool, capable of manipulating others, but easily manipulated himself...oh, and did I mention he's got a bad habit of plucking dead animal corpses out of his Compost-heap like body? And throwing them for target practice with his breath weapon? Yeah...he's...special.
The party has exploited his shortcomings to their own advantage, however, getting the dragon to offer them small favors in exchange for the eventual right to use the Evolution Engine. In the time he's been with the party, Zardozan has flown members of the party to various locales, used his magical abilities to conjure food and booze for a celebration the PCs held during downtime, helped fend off an army of high-level Yuan-ti and Lizardfolk attempting to retake the temple, and staged raids against the Lizardfolk encampments in the nearby swamps on their behalf.
To be fair, however, the drunken celebration was actually interrupted by the army attacking the temple. The party fighter, the two roguish types, and the dragon were all sitting on the temple roof, playing at target practice and getting drunk when they spotted a strange green glow from the woods...
Subara (the party fighter): "Hey, do you shee a funny light in the woodsh over there?"
Zardozan: *hic* S'not funny. It's the energy shigna- er...shignature of a tel-e-portation spell"
Subara: "...Oh. That's no good."
During the course of the fight, Zardozan was targetted by a squad of Yuan-Ti abominations who all threw their Baleful Polymorph ability at the dragon, (he's gotta roll a 1 sometime) and thus turned the fearsome creature into a tiny viper until such time as he could slither over to the party and get a dispel.
So, yeah, I'd say he's a memorable dragon.

My Players seem to enjoy interacting with him, in any case, judging by their comments.
In any case...as a player, I've had quite a few encounters with Dragons. Most of them have been pretty standard, but one campaign stands out in particular. Essentially, all the players started out in a mid-sized town which served as a trading post between the Dwarves and the rest of the continent. My character was the son of the town's most successful merchant of Dwarven steel, and as such had quite a bit of access to money and equipment, as well as good sense for business and a greedy streak a mile wide (this will all become relevant later). Early in the campaign, the town was assaulted by Orcs, and it was established that the schoolteacher was a powerful swordsman with some arcane magic. As the campaign progressed, we discovered a well with healing properties (also important later) and ventured into the underdark, and found a mercantile town there run mostly by evil creatures (Kuo-Toa, Drow, Goblinoids, as well as humans, dwarves etc.) Looking for work, we signed on as caravan guards for this red-haired merchant who seemed somewhat shady, and one of our spellcasters announced her suspicion that he was actually a young red dragon. Suspicious, we opened up the supply crates and had our spellcasters identify one of the braclets we were guarding. It turned out to be an item of Cold Resistance keyed so that it would only function for an Orc wielder. We also found fire-based weapons, and other orc-specific items. Putting two and two together, we realized that the Red must be supplying weapons to the Orcs who'd attacked our home.
Here's where things started to go south. Our party fighter was this hulking death-machine with a scythe. Even as a 5th level character, the potential for a coup de grace killing even a high-con creature was pretty good. My character, being both greedy and with a vested interest in stopping the orcs, suggested sneaking into the red merchant's lair, and stabbing him while he slept. We went through with the plan, but as the "merchant" died, his form shifted and twisted into a bugbear, and from behind us, we heard the sound of slow, deliberate clapping. We turned to find the merchant staring at us with a bemused, evil grin, and the obvious upper hand. The typical hero vs. villain banter insued, and we were essentially given an ultimatum...kill the schoolteacher in our home town, or see the whole place razed to the ground before we all die slow, painful deaths. Apparently, the red merchant had reason to believe that the teacher was actually an agent in the service of a silver dragon, and wanted him eliminated, and was willing to spare our lives if we would perform that service.
Returning to the town, we met with the schoolteacher and explained the situation, saying we had no intention of killing him. He didn't take it well. However, it became clear as the conversation continued that he didn't fear our attempts to kill him, and was more worried about the weapons being sold to the Orcs. It was at this point that a couple things became clear. First of all, Orcs would only need cold resistance items if they expected to be attacked with cold...like the breath weapon of a Silver Dragon. Secondly, the teacher wasn't just an agent of the silver dragons, he *was* a Silver Dragon, polymorphed into human form, and the orcs were attempting to drive him and the humans under his protection (our whole town) out. Armed with this knowledge, we worked with the silver dragon to plan the town's defense, although he maintained that he would not fight the Red for us.
My character's father was out of town on business, and so I took the liberty of liquidating a shipment of adamantine weapons and shields from the warehouse, and used them to finance the hiring of 30 or so mercenaries (including one spellcaster of at least one level higher than us). We fortified the stone warehouse building, and gathered as many allies as we could for the inevitable attack of the Red Dragon. It wasn't until he showed up that we realized how deep we were in. He was a Young Adult. Something like 18-19 HD. We're level 7. We eventually goaded the creature onto the ground, to stick his head into the warehouse and try to breath-weapon us. Once there, we unloaded as much Cold damage as possible into him, and our scythe-fighter managed to get a lucky crit, which put the Dragon at about half it's HP at the end of round 3.
...At which point the Red Dragon ran, south, toward where the Healing Well was. Knowing that he would return within an hour, fully healed, we talked our Silver Dragon ally into assuming his true form, and taking 8 of us (mix of PCs and the most powerful of our mercs) to the healing well to try and intercept him. We fly in, only to find the Red already lapping up healing water, and looking quite refreshed, but still unaware of our presence. It is at this point that the scythe-fighter looks up at our silver dragon friend and says "Throw me".
Expending a hero-point, our tank was hurled across the battlefield, dealing thrown weapon damage as he impacted into the red dragon's flank from the silver's throw, and then, on a second lucky crit of the night, did a huge amount of damage to the dragon. Initiative is rolled, many of us beat the Dragon, and one of our casters manages to crit with an Icebolt spell (conjures a shard of ice that does piercing damage, accompanied by a 'cloud' of cold damage) and once again, the Dragon is at about half HP.
...and then everything went to hell, as an acidic breath weapon washed over our Silver friend and all of us still hitching a ride. We look up to see the invisibility spell dropping to reveal a Young Adult Green Dragon. Now, we realized who was the real mastermind behind the Orc attacks on our village, and who was financing all those expensive magic items the Red Dragon had been selling to them. As the battle continued, the humans took the fight to the Red dragon, while the Green and Silver locked into a contest of tooth and claw and point-blank breath weapons. Things became even more grim as a flight (6) Half-Green Dragon Giants arrived to assist their mother, but the same caster who had blasted the Red so fiercely before decided to put his charisma to good use. In mid-fight, he started trying to talk to the Red Dragon. "Look, you're a smart guy. You know you can take us down, but it's going to cost you dearly...and what's to stop your Green friend from turning on you and stealing your horde once you're weak? She's got her kids and her army nearby, and you've got no backup...you'll be easy pickings!"
Faced with the logic of the situation, the Red Dragon decided the Green was a bigger threat, and blasted the Half-Dragons with his breath before attacking the Green. We rallied around our badly beaten Silver friend, who pulled out a one-time use magical item of a spell called Bring Down the Moon, which not only healed us, but also refreshed our "x times per day" abilities, including spellslots...which allowed us to turn the tide against the remaining half-dragons who were still very much a threat. In the end, the Green Dragon managed to knock her Red rival unconcious, and was cut down by the Silver as she attempted to flee. After routing the half-dragons, our party fighter finally managed to coup de grace the Red Dragon, which killed it, as I had predicted it could.
Unfortunately, the Silver Dragon was now in a position to dictate terms...namely, claiming the Hoards of both dragons for himself to recoup the cost of the magic item that had saved us all, and essentially indebting us to him and the wider cabal of Silvers of which he was a part. In the end, however, it was a small price to pay for a memorable victory. To this day, the players in that game remember the "Christmas Battle" between Red, Green, and Silver, and the poor PCs caught in the middle.
Robert "Wow, this has been a long post" Ranting