I really enjoy all of the watch books, and i've grown to know Fred Colon, Nobby Nobbs, and of course Sam Vimes. Absolute awsome. Also, I was shocked to see that, when I looked at the list of City Watch books, that I had read all of them. AWSOME! But I wish there were more...
The Death books are also highly entertaining, and death reminds me of vimes in a way.
Unfortunately, I simply don't enjoy any of the Witch books, and I haven't read nearly enough Rincewind.
And, a final note, For those wishing to become acquainted to the series, I recommend the dicworld Omnibus's, or Omnibii, or whatever. They Each contain a three select stories, and each omnibus is devoted to a particular subject. So far, I have found the Watch Omnibus, the Death Omnibus, and the Gods Omnibus, but I'm sure there are more.