I haven't seen any simplified d20-based set of rules that struck me as particularly good. Some of them are OK, but none are really outstanding. So I tend to look for non-d20 sets when I want a solid, simple set of core rules. BTRC once published (and possibly still do, no idea if they're still in business) a fairly generic game called "CORPS", which has a unified mechanic that's pretty innovative and simple to pick up, it's traditionally the set I use when I want to convert an older setting without using some custom rules set. Another good choice is the rules system used in HeroQuest, the recent Glorantha-based RPG - it's a narrative system, so it's not too hard to take the system out of HeroQuest and apply it to just about any genre.
My third choice for a simple rule system is MegaTraveller. People get hung up on the complexity of the ship and world design rules in MT, but the actual task system used to play out a session is extraordinarily simple and flexible. The CODA system, used in Decipher's "Lord of the Rings" RPG isn't too far off from the MT task system, I've been thinking of using that as a basis to convert magic and monsters into MegaTraveller and run some kind of space fantasy epic.
Or for a whole bunch of ideas on simple games, try the 24 Hour RPG site. By their nature (games designed, written, and published in one 24-hour period) those games usually feature simple mechanics. Some of them are pretty innovative, others are, well, fun to read.
My third choice for a simple rule system is MegaTraveller. People get hung up on the complexity of the ship and world design rules in MT, but the actual task system used to play out a session is extraordinarily simple and flexible. The CODA system, used in Decipher's "Lord of the Rings" RPG isn't too far off from the MT task system, I've been thinking of using that as a basis to convert magic and monsters into MegaTraveller and run some kind of space fantasy epic.
Or for a whole bunch of ideas on simple games, try the 24 Hour RPG site. By their nature (games designed, written, and published in one 24-hour period) those games usually feature simple mechanics. Some of them are pretty innovative, others are, well, fun to read.