GURPS is a generic roleplaying system published by Steve Jackson Games of Austin, Texas, with whom I am in no way affiliated (except for all the money I have spent buying lots of their games, which are usually quite worth it). Their website contains more GURPS info than one could reasonably expect, as well as more links to other fan-authored GURPS sites. While there is no such thing as a perfect system, GURPS is pretty good all around; it covers an enormous amount of ground with just the basic rules, and there is over a hundred supplements in existence. At some point I will write a lengthy article expressing my deeper thoughts about GURPS; for now, suffice to say that it is one of my favorite systems, and even on those occasions when I use another system, I often get a lot of mileage out of my many GURPS supplements (of which I own around 80, and none are for sale).
A tentative explanation of my opinion on the relative merits of GURPS and my other two favorite systems can be found here.
Links to GURPS stuff authored more or less by myself: