My favourite book has been The Hitchhikers Guide to the Galaxy for a while.
I also quite enjoyed Atlas Shrugged and The Fountainhead.
The best thing I read in American High Schoo was probably Nine Stories or Beowulf. In German school it was Faust, which is one of the best books ever, anyways.
I read a lot of Science Fiction when I was younger, many of the classics like Dune, Childhood's End, Rendezvous with Rama, 2001 a Space Odyssey, Foundation, Caves of Steel, I, Robot, Starship Troopers, Fahrenheit 451, Ender's Game. My favourites of those are definitely the Heinlein ones, Stranger in a Strange Land and The Moon is a Harsh mistress are some of my all time favourites.
I also love Brave New World and 1984 for different reasons. 1984 actually made me feel quite bad for a while.
A good book I read while in the US was Gulliver's Travels I enjoyed that a lot.
A good, modern German book a I read a while ago was "Herr Lehmann".
I read the Alchemist by Paulo Cohelo, though I found that a bit disappointing, two books that generated a similar feel but were on the whole a lot better imo were Γric-Emmanuel Schmitt "Monsieur Ibrahim and the Flowers of the Koran" and "Oscar and the Lady in Pink"