I like sci fis set in space, featuring aliens, but I like a 'realistic future', sort of like Mass Effect or Halo (especially the idea of an inter-species war). I don't like it when they borderline on fantasy (like say Dune or Star Wars). On top of that, I also love cyberpunks and steampunks.
MichaelMN
Favorite Answer
The Honor Harrrington series by David Weber is a good read (space combat)
The Beserker Series by Fred Saberhagen
The Ship Series (the Ship Who Sang) by Anne McAffrey (and others)
The Vorkosigan Saga by Lois McMaster Bujold.
You can get the starts to many of these series for free from http://www.baen.com/library/ - They let you read the first few books as e-book for no cost, and if you like them then they figure you will pay more for some of the others --- a win - win situation.
Noonlightangel
The Hitch Hikers Guide to the Galaxy by Douglas Adams
Molly
War of the worlds is a good old sci fi book
Anonymous
Check here... I would recommend any of these.
http://en.wikipedia.org/wiki/Category:Dystopian_novels