I thought about listing Mp3 files individually on this site but these search boxes actually work better than doing that especially the first one. Just pop in the name of an artist and a full list of Mp3's is found in seconds!
As always remember the legal stuff and how you should only listen to the song with a view to then buying the original when possible.

Gnutella Search by Artist or Title

HTTP Search by Artist or Title

FTP Search by Artist or Title

Michael Jackson Index
Janet Jackson Index
Britney Spears Index