Looking at the post below, it occurs to me that some suggestions for something a bit more thoughtful and less... nasty... would help.
A fair number of these are written for children or teenagers, which I'd say was a good thing - train them up right and they'll stay that way, or at least more likely than if you raise them on a diet of Warhammer and David Drake.
- Tamora Pierce's Circle of Magic and The Circle Opens - anything of hers is worth a read.
- Likewise Diana Wynne Jones - I'd recommend starting with Archer's Goon or Cart and Cwidder (the first book of the Dalemark Quartet). Oh, or The Dark Lord of Derkholm.
- No recommendation list would be complete without Neil Gaiman. His Sandman graphic novel series is an absolute instant classic, and American Gods raises some really interesting things about mythology and, well, people. After all, that's what everything comes down to in the end.
- Pamela Dean's Tam Lin is a modern-day retelling of the Scots legend, taking place in a Minnesota university campus in the late seventies. Besides the fantasy elements, it's a wonderful, complicated story of friendships, insecurity, and the problems of life.
- Lois McMaster Bujold writes gripping and extremely readable books about people who try to get along in a militaristic world, and to improve things for others as well. Start with Cordelia's Honour (comprising Shards of Honour and Barrayar).
More when I think of some.