Wowsers. So, I love the fact that I've gotten so many responses to this. I'd like to make a couple comments, if I may, based on this initial response.
humm, interesting, do you consider the best book you've ever read the book that wowed you the most when you read it years ago even though it may not stand up as well now-a-days (because my tastes tend to change slightly from month to month) or do you only say it has to be something you've read in your current mindset?
If it's #1 it would be either the Dragonlance Trilogy by Weiss and Hickman (when I was 13ish), Magician series by Fiest (when I was 16) or Wizard's First Rule by Goodkind (18), though I'd also add Wizard's Second Rule was the worst book I've ever read and I'm comparing that against textbooks.
If it's #2 it would half to be Information Architecture for Designers by Van Dijck (a few days ago). I don't read a lot of books, and I also don't like to ever have a "best" or "favorite" book, movie, song because there are so many factors that one could choose for a best (best what? Paper used? color scheme?) so I never bother thinking in these terms anymore. There's "I like" and "really like" or "impressed me" and that's about it.
Spriggan: I think that you captured the essence of what I was hoping for in this reply. There is definitely a shift in mindset as we grow and as we read more. At some point, there is always a "best" book that we could sound off on. I think, according to your categories, I'm looking for "impressed me". In this case, I especially appreciated your age brackets of when you read them. I'd also encourage you to try fiction again. Don't let Goodkind scare you off. He's a freak of nature, and authors like him (I would like to think) don't come up very often.
Have you tried Steven Erikson's Malazan books -- the first is Gardens of the Moon? It's another edgy, different take on epic fantasy.
MattD
MattD, I have tried Erikson's stuff. I read the first book and got the feeling that something was missing, but I couldn't put my finger on it. When I was about 100 pages into the second book I figured it out: I didn't care. I didn't care about any of his characters or what was happening. I didn't feel like I really understood anything about what was even occurring in the story. When something big happened, I was thinking "So what?" Yes, this series is huge, and it's amazingly complex, and it's actually quite well written too. I just couldn't make myself care about the story at all. So, I passed on this one. Thanks for the thought though.
And for everyone else, keep em coming. List your greats! You have a needy reader out here. Help me and others like me who yearn for great material!