FUDGE (http://en.wikipedia.org/wiki/FUDGE). Amazingly versatile, very rules-light, and endlessly tweakable.

Frankly, if they didn't keep offering me money, I'd chuck GURPS. Way too many rules and special cases. The few people who are interested in local games don't want to memorize an entire rulebook. That's the nice thing about FUDGE: it is very simple to learn.

Best part? It's free! (http://www.fudgerpg.com/fudge.html)