read Startide Rising by David Brin as rec'd above, but you MUST read the Uplift War at the same time (the two novels take place at the same time in different places). The second time I read them, I would shift back and forth from one to the next in the correct chronological sequence, it was an even better read - 'guerrilla war' lmfao
Also, the GRR Martin series mentioned above is truly amazing- it has so many threads and sub-plots my head gets dizzy just imagining it.
Never, ever read the 'Worldwar' series by Turtledove, you will never get those hours back- Turtledove just gets worse year by year, his early stuff was truly amazing though, Agent of Byzantium is a great collection to start out with.
If you want pure entertainment, read 'Snow Crash' by Neal Stephenson, it is a descriptive juggernaut
that will have you laughing for hours (especially if you are familiar with Southern California and realize the novel was written 15 years ago).
Dragonlance- read the Chronicles and Legends, and then read nothing else ever (same for the Drizzt novels, read the first 2 trilogies, then skip the rest)
Thieves World- read the original 12 novels only, the definitive best anthology series ever (each chapter is written by different authors with new and recurring characters)
I've got a couple of thousand novels in storage, but all that's a good start- oh, read William Gibson's Neuromancer trilogy, and nothing he did later.
Robert Heinlein- he had over a hundred novels, a couple of dozen are good reads indeed (Number of the Beast, and of course Stranger in a Strange land is in the top 10 all time great sci-fi novels)
ok, if that's not enough, let me know