Campaigns in a nutshell. Adventures in a sentence.

The players start out as apprentices or indentured servants to the court magi of a backwater province. He sends them on errands to gather items belonging to a vanished archmage. Each item is dangerous to the wielders sanity. Other mysterious wizards compeate for some of the items. Assuming the PCs are sucessfull their mentor slips further from sanity. Eventually the old ruler is killed by a creature of chaos, and the Magi takes over. The mysterious wizards are revealed to be invaders from the far realm, the apprentices of the vanished archmage (now an Epic Psudonatural) and the court magi who was orginally against them is eventually converted. (or talked out of his quests for more of the items)

Party enters a town cut off from magic, looking for an item that is dangerous to sanity.
In many taverns they hear stories of the town fool. He is the only one who knows where it is but only the local girl with a crush on a PC can get it for them.

Army Grunts serve at a outpost that guards the realms of men from humanoids, slowly find out that true evil comes from men, either thier superiors or the people that they are trying to protect.

An Undead Extravaganza:
In the empire of Thay in the eastern Forgotten Realms, a powerful Lawful Neutral necromancer (possibly a lich) has risen to power via a pact with Devilish forces. His plan is to utilize all the dead in the world to aid the living in the form of slave labor, freeing up the populace for more skilled, less mundane tasks. The Demons are enraged at the Devils' plot (who secretly plan to kill the necromancer and use the undead hordes to Destroy The World (TM)), and cause chaos. As the plan progresses over several decades in the East, there is economic upheval due to the rising power of the peasantry. At lower levels, the party faces evil forces engaged in body-trafficking and magical experiments, higher levels involved continental-scale travels against evil religions, and finally culminates in a battle between the forces of Good, the undead army (now under control of the forces of Hell), with the Chaotic Demons trying their damndest to destroy their Infernal bretheren whilst inflicting pain and dischord upon the surface of the world.

The Last City: The Gods die in a celestial war of Good vs Evil. Priests--losing their hold as masters of civilization--get panicky and ally with Wizards to attempt a massive, multi-thousand spellcaster ritual attempting to "Raise" the Dead gods. The magical principles invovled are poorly understood and the ritual unleashes what will become known as "The Arcanoclysm". The world is, for all intents and purposes, annihilated. Nations vanish, continents warp, previously unheard of monsters appear by the thousands, previously mundane people are infused with magical power...and Cros-Mogmun, sprawling, unimaginably immense capital city of the Grune Empire, lies shattered, warped, bloodied and bowed.

The PC's are the second generation after The Arcanoclysm and live in "The Gut", a vile and corrupt neighbourhood at the mouth of "The River of Filth".

Most uneducated inhabitants of Cros Mogmun believe that the entirety of existence is comprised of ruined City...they may be correct.

Dwarves now live beneath the city, and have devolved to a more feral existence. Their Favored class is Barbarian, and their Combat Bonuses vs Giants is replaced by an equal one vs Vermin.

Elves have diminished as well, their ancient Kingdoms destroyed. Elves in my campaign are stock D&D Gnomes, except that their heights are calculated as for humans.

Due to the effects of the Arcanoclysm, every character may take levels in Sorceror as if it were a favored class.

Some more that I'm running/have run/played in. Most are Eberron-y.:

Sharn - Freelance Police: The party is the Freelance Police, a crimefighting organization run by the Sharn Watch to deal with the crimes that are too dangerous or esoteric for the normal Watch to deal with. Although most of their cases are unconnected, the Freelance Police have become embroiled with the schemes of the Artisan, an extraplanar being who wants to recreate the Last War for the aesthetic challenge.

In the Halls of the Goblin King: Sent by House Orien as liasons to the Darguuni throne, the PCs find themselves tasked with labors from the Llesh Haruuc, who views them as a powerful ally in his own struggles against the warring factions of his fractious empire.

Morgrave U: The characters are students at the hallowed halls of Sharn's Morgrave University. This entails a lot more than most colleges do, however - research papers often take them through the depths of Sharn's ruins, and field trips are much more exciting...

Planespotting: A bunch of cutters team up, somewhat against their will, in the hopes of making a ridiculous amount of money. Along the way, they find themselves tasked with destroying a lost artifact that would make either side of the Blood War very happy indeed, and make enemies of just about everyone they cross paths with. No wonder the turnover rate of partners is so high.

Demiurge out.

The Shadow Rising - Forgotten Realms campaign in which a gnome necromancer moves into a derelict castle in Daggerdale. He sets about uncovering the three obelisks that when activated will open a portal to the Plane of Shadow and begin the process of changing Daggerdale into a shadow realm.

A math error on my part made the climatic battle a near-TPK when the necromancer snapped his Staff of the Magi. D'oh.

Child of Darkness - A half-demon man returns to Veluna to have his revenge upon the leaders of that country for their actions in banishing the demons from the world after the Greyhawk Wars. Being a child of prophecy, he can only be killed if first touched by the elemental weapons of power.

Notable because the PCs attacked the bad guy's army and then ran away, setting into motion a chain of events that caused Veluna to be totally razed to the ground. The first time I've ever seen anyone "lose" a game a D&D.

JediSoth

A Distant Mirror: Wars, plagues, and intrigues. Orcs are swarming out of the north, the Huns are preparing to sail from America to invade Europe, and a plague ship sails towards Italy with a doomed crew. Alternate history with dweomercræfting.

Okay, here's one I am currently running:

The Road Untaken: The characters come together by seeming coincidence, but discover that they all have some unexplained connection to each other. It is revealed through traumatic flashbacks that they have all been cursed with a magical amnesia by an unknown villain, and they must find out who they were, and in doing so return to oppose and defeat a powerful madman. The catch is that the villain gave them their heart's desires as their new lives: the fighter that always envied the spellcasters is now a wizard, the secretly devout rogue is now a respected priest. Will the party want to go back to their own lives, knowing that they may lose the good lives they have now?

Hey Mythus...are you using Northern Crown from Atlas Games? It might help you out on that one.

(Also, if you like Alt History and need some more campaign fodder, consider reading Marvel Comics' 1602, or The Years of Rice and Salt by Kim Stanley Robinson, CJ Cherryh's Sword of Knowledge trilogy as well as innumberable AH books by Harry Turtledove and S.M. Stirling.)

Dead Wreckening (min adventure or weird campaign):
We all have them. That one character you really liked that either go squished, eaten, stabbed, blown up , shot or stabbed. But for some reason you didn't throw the character sheet away.

The characters are dead. They are all raised as revenant spirits to deal with the enemies of the kingdom. How long will they be under the control of he that raised them and where would they go if they rebeled?

Fahgitahboutit (adventure): The Pc's are enforceers in the Orcish Mob and are hired for what starts out to be a simple job and turns into something more...

War of Nine Rings (campaign):
There are nine moons orbiting a gas giant style planet. All have life and different cultures ( fantasy with each moon acting as the home world of certain races and beasts). There are mystical gates {world bridges} thatlink the moons to each other and each one has a particular feel to it. The campaign centers around the adventures on the different moons and the politics of such a situation.

Death of Divinity (Epic D&D Campaign)
The player characters accidentally stumle upon an artifact that they accidentally use to fundamentally alter one of their patron dieties. This creates an imbalance in the heavens, and sets in motion Tiamat's plan to devour all the other gods and destroy the universe. The players are chosen by their patron dieties to serve as their agents in the war against Tiamat. God's die and the world slowly falls apart until the characters must ally with Bahamut in a final desperate gamble to invade Tiamat's realm and undo the damage she has caused. Campaign ends with either Tiamt's victory and the end of all things, or the PC's victory, and their becoming the new gods.