Arianus: Read the Assassin's Apprentice by Robin Hobb.
orcishgamer: This one too, though it's rather depressing.
yeah, that first trilogy was powerful, I was crying by the end, only book series that's made me do that.
wlmiv: For fiction I'll second a few suggestions that have already been made: George R.R. Martin's A Song of Ice and Fire series is definitely my favorite fantasy series (first book is A Game of Thrones), Stephen Erikson's Malazan Book of the Fallen is an interesting fantasy series because of the scope of the world that is imagined. I would personally find the characters and the story of Song of Ice and Fire more compelling than Malazan but I find the Malazan world and back story more compelling. Reading the Malazan books is almost like an archeological dig if that analogy makes sense. I'll also say the Wheel of Time series but the critiques about it booking tedious in the middle books is quite true (although because it was one of the first series I read it will also have a special place in my heart).
Some good science fiction: Asimov's Foundation Trilogy (read the original 3 first, he wrote prequels and later books but the original three should be the first you read). Also Asimov's Robot trilogy is quite good, each novel is basically a detective novel set in the future. I cannot recommend Robert Heinlein highly enough. Stranger in a Strange Land is my favorite of his, but many are great. I especially enjoyed The Moon is a Harsh Mistress, Farnham's Freehold, The Cat Who Walks Through Walls, Starship Troopers, and Time Enough for Love. Frank Herbet's Dune is another classic very worth reading (the first book can be read and enjoyed whether or not you ever read the sequels. Orson Scott Card's Ender's Game is another great science fiction book about children who are trained in war games to prepare for a coming war with an alien race. Arthur C. Clarke's Childhood's End is another great one about mankind's first encounter with an alien race.
Although I'm only just about to read George RR Martin's work, the Malazan Book of the Fallen series by Steven Erikson is excellent, like wlmiv says, really incredible world, his writing is darker than a lot of fantasy, and handled in an exceptional way, bittersweet and philosophical. And I as well hold The Wheel of Time in a special place. It has undeniable faults, but incredible strengths as well.
Since wlmiv mentioned them also, Ender's Game and Dune are classic in sci-fi, and similarly philosophical. Those others he mentioned, and that list by orcish gamer, are one's I'd had reccomended to me but haven't gotten to yet. They're on my list :)
Ric1987: If you haven't read the Mistborn trilogy, do that.
Oh yeah this too :)