This is a very popular notion here at SDMB, but I will have to chime in as part of the minority who did like, and even preferred the sequels.
I have to recommend 100 Science Fiction Short Short Stories. Delightful anthology of stories each less than two pages long (there’s an equally good Fantasy one too).
Knowing what non-SF books you have liked would probably help with a more catered recommendation…
When I was younger, I read a lot of Asimov. It’s probably somewhat dated, but he’s an easy read, especially his short stories.
Some of my favorites are The Man Who Folded Himself, Timefall, The Green Futures of Tycho, and Replay.
I really love Greg Egan’s stuff, especially Diaspora, but it’s very hard sci-fi, so that may or may not be to your taste. I guess it’s also not very popular since half of his stuff seems to be out of print 
I like the novelization of the Robotech series, it added a lot of depth and fixed a lot of the continuity problems.
As much as I hate L Ron Hubbard for his Scientology crap, and as much as I couldn’t past page 2 of Battlefield Earth, I did read his 10 book Mission Earth series and found it to be a very enjoyable sci-fi satire.
I would definitely, if you don’t mind humorous sci-fi, insist you read the Hitchhiker’s Guide to the Galaxy series! I would also check out his one non fiction book, Last Chance to See, which has similar absurd characters except they happen to be real people 
The Memoirs of Elizabeth Frankenstein is an interesting feminist quasi-pagan take on the Frankenstein mythos.
Possibly more fantasy than sci-fi, but the books of Michael Ende are all wonderful, especially Momo and The Neverending Story.
The Ecstasy Club is an interesting genX novel with cyber themes by Douglas Rushkoff.
You might also want to check out some graphic novels. I recommend Watchmen, The Invisibles, Club Zero-G and Testament.
Michael Chrichton has some readable stuff, altho in later years it’s starting to get full of whatever his personal rant is at the time to the detriment of the writing. I also recommend his non fiction book Travels.
Fifth Sacred Thing is another thought provoking novel for the ecofeminist.
Tom Robbins books are excellent and quirky, perhaps similar to Douglas Adams, but perhaps not truly sci-fi.
Stephen King and Dean Koontz are more strictly horror, but some of their stuff has sci-fi elements. I would take a stab at the Dark Tower series.
Cory Doctorow is a great relatively recent author with some cool ideas.
William Sleator’s stuff is great if you don’t mind it being lumped in with ‘young adult’ books in some places.
I’ve heard Snow Crash is one of the must reads of the cyber genre. I read and enjoyed Vurt.
Creator is only loosely scifi but a great read that was made into a movie.
Philip K Dick stuff is great if you’re into that sort of thing (I am), but if you’re not into mind-bending psychedelic and cold war paranoia sci-fi then steer clear
Try either Bladerunner (aka Do Androids Dream of Electric Sheep, or one of his many short story collections.
The original novel that Contact was based on was also great.
A lot of Ray Bradbury’s stuff is sci-fi and a good easy read, tho some of it is a little dated. I would check out his short stories and the Martian Chronicles.
That’s all I can think of right now…