I took a SF literature course back in college. The prof had a difficult time coming up with a reading list because he figured anyone taking the class would have already read a lot of SF. So he was looking for obscure but good books. Most were really good reads, so I figured I'd list them here for anyone who might be interested. Off the top of my head, I can recall:
Canticle for Leibowitz by Miller. I liked it a lot.
Where Softly Late the Sweet Birds Sang by Wilhelm. I liked it a lot.
Childhood's End by Clarke. Good read.
The Forever War by Haldeman. Excellent.
The short story
The Star Thrower by Eisley. Not a fun read, but the kind of thing you would expect to be given to read in college. Weighty.
There was another Clarke book in there. It think it was
Rendezvous with Rama. Not one of his better novels, but worth reading.
I think the prof might have given us
Neuromancer too, which was not obscure at that time. Neuromancer is an important book, because it predicts a lot, but I never liked it that much. It's had a lot of influence in pop culture though.
There were about 5-6 more, but I can't remember which ones they are. I've read so many on my own.