http://www.aimster.com last time I checked.
I keep meaning to download Morpheus, but I never get around to it. However, my friends have it, and tell me that as well as being upgraded, Morpheus also now shares its database with Casa (or Caza or something, I've never seen it written down). Casa is meant to be much bigger and better, though, as it also has its own database as well as Morpheus's...