I liked the Foundation series. I didn't read the whole series (missed 2 books) and Asimov died partway through writing them but they're good. Make sure to pick up one of his short story collections too, like Robot Visions.
Ray Bradbury is another classic writer, most famous for Fahrenheit 451, but he did some other short stories I liked too.
If you like classic science fiction then you'll probably like The Island of Doctor Moreau with it's tribal undertones and When World's Collide, another classic. A lot of Jules Verne's books are pretty cool, you might have read his most popular works like Around the World in 80 Days, Journey to the Center of the Earth, 20,000 Leagues Under the Sea, etc. A Trip to the Moon and Around It is kind of a cool book, if you aren't bored by all the math in the beginning. I read through the Foundation series in the beginning of the summer and I've just now finished 6 or so Jules Verne's works off of Project Gutenburg and have a few left to go. I'd recommend getting them at a library instead of off of Project Gutenburg though, the ones off of the Internet are sometimes taken from a more direct translations (which are usually older). While it's closer to the original book it's also harder reading and you'll probably want a dictionary and encyclopedia on hand when they start throwing around the names of 19th century bookbinders.
The Ringworld series inspired a some other books and games, although I'm not a huge fan of them. Read the first book and if you don't like it then skip the rest. The first book of the Ender's Game series was required reading at my high school, so I guess you could read them if you haven't already.
Oh and 1984 and Brave New World if you haven't read them in school.
This is a fancy, fake-leather-bound, gold-lettered copy of The Ultimate Hitchhiker's Guide, which is a compilation of all five books in the Hitchhiker's Guide to the Galaxy series by Douglas Adams. It's a very good book. I just finished it maybe a week ago.
If you squeeze it sharply, you can hear the air hissing out from the space in between the "leather" and the cardboard. :D
Oh yeah, read this too.
