For a good triology I suggest Dean Koontz's Frankenstein. It has very little to do with the original Frankenstein book, and comes out a lot better because of it. As far as I know, the third book isn't out yet, but I've read the first and second and enjoyed them a good bit.
My problem with Koontz, though, is once you've read a lot of his books they all start feeling extremely similar, almost as if you're reading the same book with different characters and events. He writes extremely well, though, so it's forgivable.
Kiterunner is one of the best books I've read in a long, long time. Simply astounding.
I read Wheel of Time until about 1/3 of the way through book 8. It just got too damn monotonous. Bodhi is right though, it was great until about book 6.
Another great sci fi / fantasy trilogy is The Coldfire Trilogy, by C.S. Friedman. Unlike, say, The Wheel of Time, something of imortance seems to be happening all the time. Every event is given an appropriate amount of weight, so the books never seem to grow stale. Also worth noting is the emphasis on character development, which adds a layer of depth that's nice to have. To top it all off, it takes place in an amazing world, and puts a nice spin on the whole "magic" thing. I recommend it.