I think the core base classes can do more than some people credit them with.
For instance, the problem Henry poses: an effective swashbuckling fighter is only a problem if you assume that he needs to be a swashbuckling fighter. Make him a Fighter/rogue and the viability problem goes away. If you think "he's a fighter so he has to be able to stay in one place and trade damage without any other allies on the front line and he can't have any classes other than fighter, of course you're going to have trouble. If, on the other hand, you go for a fighter/rogue, you can make an effective "swashbuckler" who dances between opponents wearing a mithral chain shirt and dodging blows, then jabs their opponent with a mortal thrust when they make a mistake.
Human Ftr 2/Rog 4, Weapon Finesse, Weapon Focus: Rapier, Combat Expertise, Dodge, Mobility, Spring Attack. With a buckler and rapier, you can get an AC rather similar to Mr. 2 handed power attack (buckler+chain shirt+16 dex=AC 18; fullplate=AC 18) and, provided you have a flank or a flatfooted opponent, you can do quite significant amounts of damage (3d6+str+enhancement vis a vis Mr. Two Handed power attack who probably has 2d6+ (1.5xstr--probably +4), + enhancement + Weapon specialization). And if you get fireballed, you evade. Increasing in levels, you'll pick up a few other feats (maybe whirlwind attack or Improved Feint and weapon specialization) and start to get more sneak attack dice.
Fighter/bard or just plain bard with perform: witty reparte (oratory) can also work as a swashbuckler. (And he can even two-handed power attack with his longsword if he wishes). In D&D though, you'd need to rely pretty heavily on magic in order to make the fighter/bard combat-effective and if your concept isn't fighter/magician then it might not work.
Just plain fighter might work for a slightly different kind of swashbuckling hero--more Will Turner than Errol Flynn: Fighter X. Weapon Focus Longsword, Weapon specialization longsword, power attack, dodge, mobility, spring attack, combat expertise. Wearing a breastplate or chain shirt and wielding a longsword (with a buckler in the off-hand for when he wants two handed power attack damage), this character fights with strength as well as finesse. Still, I think he can look the part of a swashbuckler in a fight as well as out of it. His AC isn't as good as the guy who wears fullplate but he has options other than standing toe to toe so it will often balance out.
None of the characters fill exactly the same role as the two handed power attacker but then you don't want to. I doubt you'd be satisfied if the DM said "OK, well, I'll let you do 2d6+1.5x str bonus 19-20/x2 crit and get two handed power attack with your "rapier" and I'll let your "chain shirt" give you a +8 armor bonus if you live with a +1 max dex and pay 1,650gp for your "chain shirt." You want to have a fighting style that is different from Mr. Two-handed power attack but still to be able to do a similar amount of damage and survive for a similar number of rounds. That's where prestige classes and other non-core material come in. I don't think they're strictly necessary to simulate the various archetypes but they can help to give a little more flexibility to the various archetypes.