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

Real MP3 Finder
http://www.saphware.com/mp3finder/index.html
Software based meta crawler

2 Find MP3
http://npssoftware.com/2findmp3/
MetaCrawler software that searches both http and ftp and verifies the results. It is compatible with most ftp software.

Abe's MP3 Finder
http://www.abes.org/mp3finder/index.html
Searches gnutella, scour exchange and ftp servers simultaniously

MediaGrab!
http://www.eastbaytech.com/mediagrab.htm
Finding media files from the web, Usenet and more. Instead of using a web page search engine to search to find multimedia files, you can use MediaGrab!

MP3Fiend
http://www.mp3fiend.com/
Metacrawler software that gets it's result from top search engines and offers compatibility with software like cuteftp, go!zilla and Get Right

WinMP3Locator
http://www.winmp3locator.com/flash/default.asp
WinMP3Locator is a software based meta crawler

MP3 Easy
http://www.mp3easy.co.uk
Search songs by title and artist and has functionalities like asking songs in return for the ones downloaded from you.

Iwan's MP3 Finder
http://www.geocities.com/yulhaedir/mp3find.htm
A FREEWARE program enabling you to search up to TEN MP3 search engines simultaneously, or display the results of up to FOUR MP3 search engines on one screen

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

WinMp3Locator
http://www.winmp3locator.com/
WinMP3Locator searches for a song by the user-specified keywords in all popular MP3 search engines

ComTry MP3 Downloader
http://www.mp3downloader.com/
ComTry MP3 Downloader helps you to find your favorite MP3 files on the internet.