Yeah, I'd say Childhood's End is probably my favorite though Rendezvous with Rama is a very close competitor. The City and the Stars was also very good, though I thought it got a little silly in the second half. Really, it's difficult for me to choose one. I've read plenty of sci-fi by a variety author but I always seem to come back to Clarke for his awe-inspiring imagery and extremely optimistic view of the future. Also, I have always liked the idea that he was a scientist first and writer second.
I've read a decent chunk of his novels mind you, but I'd still like to read more. Got any suggestions?
Here's a list of the ones I've read (in chronological order no less):
Childhood's End
The City and the Stars
2001: A Space Odyssey
Rendezvous with Rama
2010: Odyssey Two
2061: Odyssey Three
Rama II
The Ghost from the Grand Banks
The Garden of Rama
Rama Revealed
3001: The Final Odyssey
The Trigger
The Light of Other Days
Time's Eye
Sunstorm
Firstborn