I pretty much only use Bittorrent via Azureus. Rarely I might use Xfactor, which connects to Fasttrack (Kazaa), OpenFT and Gnutella at once, but I rarely steal songs and smaller files like that.

I have eDonkey2000 installed, but I'm not a big fan of the client, so I pretty much only use that if I want to nab something I can't get otherwise. Maybe if someone makes a worthwhile OS X-native port (no Java), I'll use it more.

My ISP NATs me, so I never get a decent upload ratio when I P2P.

http://azureus.sourceforge.net/
http://www.xfactor.cc/
http://www.edonkey2000.com/