Sam Vimes, of course, although I think the echo of that name has already bounced around the thread quite a few times. Apart from being fantastically dark and cynical, he's actually a great source of inspiration to a young lad going through his teens, with his rigid moral code and assorted imperfections. To say that Vimes is a three-dimensional character would be an understatement; even Cthulhu would get dizzy looking at all his odd angles. And the way he loves Sybil, so wonderful.
I kind of started at the wrong end of the series, what with the first Discworld book I ever read being Hogfather, closely followed by Thud! A good entry-point, though, would be the Tiffany Aching series, with the Wee Free Men, ("Crivens! Whut aboot us, ye daftie!") who should have been an option in this poll, although I suppose that it might be out of respect for their fear of having their name written down that they were left out.
Then we have Vetinari, DEATH, Granny Weatherwax and witches, the UU faculty, OOK! and naturally all the other members of the City Watch. Gods (Blind-Io, the Lady, Offler and so on), I love Discworld and I hope that Sir Terry lives long and well, providing that they find some kind of miracle cure for Alzheimers. Long live Sir Terry Pratchett, a master words and narratives, a lord of comedy!