The Andromeda Strain, by Michael Crichton
Cities in Flight by James Blish
Stranger in a Strange Land, Time Enough for Love and The Number of the Beast, all by Heinlein
I'm going to throw in Star Maker and Last and First Men by Olaf Stapledon, and The Martian Chronicles by Ray Bradbury.
I also cite Larry Niven's Known Space books, notably the Ringworld series but also Destiny's Road; Alan Dean Foster's Humanx Commonwealth series; and William Gibson's books Burning Chrome, Neuromancer, Count Zero and Mona Lisa Overdrive. I loved The Difference Engine.
I also like Gibson's Virtual Light series Virtual Light, Idoru and All Tomorrow's Parties.
A long time ago, E E "Doc" Smith wrote a lot of space opera stuff. I know the Lensmen series are probably the first thing people think of - but I'm going to cite the Family d'Alembert series as my favourite Doc Smith series instead. Secret Agents, loyal to the Empire, operating under the guise of a travelling family circus? Priceless.
Finally, I love anthologies of short stories; Alan Dean Foster's With Friends Like These ... and ... Who Needs Enemies?, John SHirley's Heatseeker; and Pat Cadigan's Patterns.
Oh, and Mirrorshades: the Cyberpunk Anthology, Alien Sex edited by Ellen Datlow and Mathenauts, edited by Rudy Rucker.