The Man in the High Castle by Philip K. Dick is my all time favorite. Also a big fan of Zelazny and Bradbury. I guess I started really reading sci-fi around age 13 (I'm 23 now). Kind of graduated to sci-fi from pulp fantasy (not that there's anything particularly wrong with fantasy, pulp or otherwise).
Oh, and while we're on the subject of sci-fi writing, I think I'll add a gratuitous plug for one of my favorite sci-fi publications,
On-Spec,
a Canadian-based speculative short story and poetry magazine. The story quality is high, the voice tends to be uniquely Canadian (although On-Spec is not a Canadian-only publication; submissions are accepted from anyone who wants to send one in) and there is plenty of content for the money (four issues a year, each running 100 pages plus). Anyway, I just thought I'd put the word out there, especially to fellow Canuks who might be interested. I'd recommend the mag to anyone though, especially to you Americans with that kick-*** exchange rate!
Anyway, great thread LCC, it will be interesting to see what some of the other SIEV players out there are reading.