That's the whole trouble. You can't ever find a place that's nice and peaceful, because there isn't any. You may think there is, but once you get there, when you're not looking, somebody'll sneak up and write "Fuck you" right under your nose.” - J. D. Salinger
Their stuff is so diverse it's hard to say. I love wish you were here and the wall. Another brick in the wall parts 1 and 3 are better than 2, but 2 gets on the radio because the "we don't need no education" thing is catchy. If you tend to like weird songs, get some of the early syd barrett stuff. Animals is their most political CD. The wall is something anyone should have -- I tend to get impatient with neverending solos and other things progressive bands are prone to, but I can listen to the wall all the way through. Without knowing you my suggestion is to get Echoes, and then get the CDs your favorite songs on that are from.
listen to "dogs" off of animals. the wall is pretty accessible too. don't listen to dark side of the moon unless you could sit down and just listen to it all the way through. it's quite an experience.