Ever heard of the novel "East" by Edith Pattou? I think she uses 3 different 1st person POV (at least). It's one of my all time favorite books. Also "Zel" by Donna Jo Napoli (which I really enjoyed) uses several first person POV as well. Rob Thurman likes to defy rules though. I'm several books behind in her series, but I remember being impressed with what she was able to do stylistically in the first book.