Haha, a thread about books! Finally my kind of thread! (I'm a sci-fi addict)
Let's see...
Stranger in a Strange Land by Robert Heinlein - Favorite book ever by one of the best authors of all time.
Anything by Isaac Asimov
The Bio of a Space Tyrant series by Piers Anthony. I know he usually writes fantasy, and the Xanth series is repetitive enough to turn anybody off, but this is an awesome space opera series.
The Deathstalker series by Simon R. Green. More space opera, fucking awesome.
The Hitchhiker's Guide to the Galaxy. Whatever you do, don't watch the movie.
ALL of Terry Brook's novels.
The Wheel of Time series by Robert Jordan. RIP.
The Lost Fleet series by Jack Campbell.
Scar Night by Allen Campbell. Don't read the sequels, they'll only let you down.
Battlefied Earth by Ron L. Hubbard. I know this nutjob founded scientology, but this book is epic.
Solaris - Stanisław Lem, An attempt to understand a alien life form their experiments provoke a strange reaction. Nothing made from this novel has anything near the impact of the book itself.
Amazing fucking recommendation. You get major kudos for that.