The Joshua Tree came out at exactly the right time -- I was 17 and stuck at an all-male boarding school in the middle of nowhere, with nothing to do but play rugby and take cold showers -- so that's the one that's really stuck with me.
(Have also got a weird soft spot for Zooropa as it was one of the only cassettes in the fucked-up VW van that I drove around Europe with a couple of university mates in the summer of 1993. Got us from San Fermin all the way to the Oktoberfest, although Daddy did not (in fact) pay for our crashed car when we hit a goat, then a tree, in the Algarve.)
Oops! Listening to Dinosaur Jr. -- Without A Sound