Pathfinder

I've been looking fairly recently at Pathfinder, a game system extremely close to Dungeons and Dragons, but with (in my opinion) a significant number of improvements.

It is 100% compatible with D&D 3.0 and 3.5, but just has some nice fixes here and there. (Stealth being a single attribute in 4.0 was done long ago in Pathfinder. Class progression is usually smoother. Balance is shifted around a little).

Anyway, putting up a link to Pathfinder's SRD, in particular, those familiar with D&D should look at how they've improved the Arcane Archer, and Arcane Trickster.

Most impressive however to me, is how they have changed Sorcerer as Rob was saying. There is now actually a reason not to take a prestige class when you're a sorcerer. Before, not multi-classing as a sorcerer was ALWAYS a disadvantage, without exception.

I think if I ever run any D&D games from now on, it'll be Pathfinder as the base system.