I love Clifford Simak, who seems to have fallen along the wayside. Except for some clunky early and late books, I love them all, particularly Goblin Reservation and Way Station.

I love recommendation posts, it gives me lists of things to track down--and old stuff is often available online!

I read The Moon Is a Harsh Mistress in -- high school, I think. I remember being fascinated by the mechanics of how to create a society on the moon. The story itself was good but not spectacular. Very much a "literature of ideas" story, and the idea alone was just enough to sustain one novel. A different writer (I vote for Resnick) could probably have turned the idea into a series, but not Heinlein.

So far every item on the list brings back happy memories. I do think Heinlein's ideal society has been given its fair shake in Somalia.

I'm loving the lists and nodding a lot. Feeling too stupid to add much. I'll weigh in for Short stories: McCaffrey's "The Ship Who Sang," Mieville's Novella "the Tain." and the stories in Looking for Jake, Stephenson, Gibson, Cadigan (Synners in particular), second Vinge's True Names, Greg Egan's Disaspora series... more after I sleep some.

Don't know if qualifies as classic but Doris Egan's Gate of Ivory series. She is now a TV/ writer producer.

You know who we've left out? Hal Clement! I loved Mission to Gravity when I was a teen.

Also Larry Niven's Ringworld, and probably Tales of Known Space. Oh, and The Mote in God's Eye, which he wrote with Jerry Pournelle. (BTW, Jerry Pournelle's daughter wrote a sequel to MiGE, which challenged/overthrew a lot of icky subtext in it. Came out just recently.)

Alexei Panshin's Rite of Passage. John M. Ford's Growing up Weightless. Suzette Hayden Elgin's Native Tongue.

While not precisely classics, we can't leave out Lois McMaster Bujold. If you have been deprived, I'd say start with Cordelia: Shards of Honor and Barrayar.

I had a terrible crush on Poul Anderson's Captain Sir Dominic Flandry as a teenager.

Consuela has mentioned some great books. Mission of Gravity is often cited as one of the best books from an alien point of view. I must differ on The Mote in God's Eye, because of the supposedly brilliant female scientists who turns into a screaming idiot. Jerry Pournelle is in the running for "Most Sexist Author."

Did he ever write a Gor book?

RA Lafferty short stories. He was a huge influence on Neil Gaiman and was a fantastic writer who is also great fun to read. 900 Grandmothers is one of my favorite books, which I would definitely recommend you buy, except that I see it's scarily expensive on Amazon.