I just finished Pratchett's Going Postal. I have liked some of his others better. Also Orson Scott Card's Crystal City and Diana L. Paxson's addition to M.Z. Bradley's Avalon books, Ancestors of Avalon. Sometimes you just have to keep reading a series.

I have 2 books going right now: Land of the firebird : the beauty of old Russia by Suzanne Massie in preparation for a trip to Russia; and, For the glory of God : how monotheism led to reformations, science, witch-hunts, and the end of slavery by Rodney Stark.

Of books mentioned, I really liked Guns, Germs, and Steel.