George RR Martins Game of Thrones is probably the best fantasy series i've ever read.
Stephen Donaldsons Gap series is the best sci-fi by miles but not for everyone.
LOTR, well nothing to say really - it's unassailable. Cannot believe Jackson didn't do Scouring of the Shire, it's the whole point of the book! Still awesome films though....
Comedic sci-fantasy? Nothing better than Douglas Adams (RIP) or Pratchett - Good Omens was the best take on religion i think i've read.