I just finished the Rama series (Rendezvous with Rama, Rama II, Garden of Rama, Rama Revealed) and have to say I enjoyed it.
Rama II was the worst book of the four but it improved dramatically since then. All of them have interesting insights into human behavior and addresses some religious issues (and Clarke was decidedly in favor of a God, though he portrays God differently in the last book). But as a story over all, still very good. He does a good job of tying in external references, while still building a world of his own, and making the story believable with the way people act and react.
Worth the read if you like science fiction and probably even if you don't.
Next I"m starting The Dungeon by Phillip Jose Farmer.