I´m really looking forward to read about the witches (all of them). I already have Wyrd Sisters on my shelf. I might still have a square left where I can use that one :D.
Personally I love all the books with the Night Watch (especially Vimes) in it (except the last book). Mort and any books with DEATH in them are fun too.
I´ve actually read two of the Night Watch books and Guards, Guards I really enjoyed. Men at Arms was the other one I think and this was merely an okay book for me. But I think I will reread both of them at some point.