I like the Hero System, but be warned: it's a big book. With small print. In other words, instead of being a picturebook with a few rules thrown in for flavor ::cough:: D20 ::cough::, it's a truly generic, yet fully described AND easily customizable 'engine' for roleplaying. You have to do most of the flavor and actual creation details yourself, but if you're like me, that's a good thing.
It's also a tad expensive, but you can find it on Froogle for much cheaper than MSRP. There's also a review on RPGNet. If you have any other questions, let me know.
