SongSpy
http://www.songspy.com/
A peer-to-peer software tool with it's own network and many napster-like features (for example a built-in mp3 player)

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

Audio Galaxy
http://www.audiogalaxy.com/
Both software (sattelite) to 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

Filetopia
http://www.filetopia.com/
Another tool with it's own sharing networks but offering real good security and levels of sharing. Has integrated email and im.

iMesh
http://www.imesh.com/
Yet another tool with it's own sharing networks. Many cool features like animated skins. Worth a try

Aimster
http://www.aimster.com/
Integrates with your AOL Instant Manager and let's you search Napster, Gnutella, AOL and MSN networks for files

eDonkey 2000
http://www.edonkey2000.com/
eDoney 2000 is a multi platform file sharing tool with it's own network. It can find any type of file, resume downloads, get one file from different sources simultaneous and has many more advanced features.

Abe's MP3 Finder
http://www.abes.org/mp3finder/index.html
Abe's mp3 finder searches gnutella, scour exchange and ftp servers simultaneously