Tricky question. Catch-22 is a very good book, although I found it a bit hard to get into, however that was a long time ago, I imagine if I tried again now I might find it easier.
I'm going to be epically bias here and recommend The War of the Worlds. It's a good read, well described and opens up some questions about the sociopolitical goings on at the time the novel was written (Colonization being chief among them).