Zeropaid has a nice list.
http://www.zeropaid.com/programs/top_mac.php
Limewire is a good Gnutella client so it should be good on a Mac. And Azureus is fine for Windows so it's worth a shot as a Bittorrent client.
And I've seen this around.
http://www.softpedia.com/get/UNIX/Ne...ns/aMule.shtml