Fallout
GURPS would make a lot of since, because the original Fallout games by Interplay were originally supposed to be powered by GURPS. The FalloutPnP, if you read into it, is actually just the rules, equations, statistics, etc. that were used in the first game. So running a game in that system is exactly like playing the first two Fallout games. I'd be down for either, or another system--I love Fallout.