Audio Galaxy
http://www.audiogalaxy.com/    
Search user collections at their own machines and a web based search through user's personal online collections, which resides on the Audio Galaxy servers

KaZaa Media Desktop
http://www.kazaa.com/
Another all-format peer-to-peer file sharing tool with all the usual features and it's own network

Gnute
http://www.gnute.com/
Don't want to download software but do want to access the gnutella network? Gnute is a web based search engine that let's you search the gnet

Findsongs/Palavista
http://www.findsongs.com/
A MetaCrawling web-based search that looks to ftp servers for it's results

Scour
http://www.scour.com/
Scour is one of the oldest mp3 search engines on the web, although it has gone through many make-overs.

OutLoud.nl
http://www.outloud.nl/
A dutch community/news style website that offers a number of free mp3's, mostly unknown artists though

MP3.com
http://www.mp3.com/
One of the most complete mp3 portals out there, which also offers free mp3 music by mostly unknown artists

SearchLord
http://www.searchlord.com/
Searching the visible and invisible web via multiple vertical metasearch engines, specialty searches and web category subjects.

Freegle
http://www.freegle.com
Freegle is a web-based search that crawls Freenet. It is still heavily under construction but worth a try

UdoRadio
http://www.udoradio.com
UdoRadio was created by a small group of people that were generally dissatisfied with streaming and download audio sites on the web.