Liz t.s.Pratchett is one of my favourite authors. Everything that everyone has been talking about on this thread and more.
I'll reiterate from the Marion Zimmer Bradley thread, too. I have enjoyed every book of hers that I have read, and that is lots, although not all.
Helen
P.S. the only thing I miss about not being a librarian any more is that I don't get to buy (and read) lots of really good books for the library. Spending public money for the edification of the public, etc etc