I've read one of Pratchett's books, Going Postal, which is number 25 of his Discworld series. I haven't been able to read more of these books for some reason - the writing seem forced and the humor obscure.
But I really enjoyed The Wee Free men, about a young girl who enlists some very strange allies in the search for and rescue of her younger brother. The funny parts are funny, and the descriptions of a world that is strangely intersecting ours are quite wonderful. I have the sequel on my iPod and I'm looking forward to reading that.