MusicLover is a brand new (as in, only a few days old) application by Dave Watanabe. Dave Watanabe is the author of renowned Macintosh applications Acquisition for Gnutella, Liberty for Fastrack, and iBug for iTunes Internet Streaming function.
MusicLover uses echocloud.net's database of artists to quickly find and reference lists of artists similar to the search item. I use it primarily to broaden my musical horizons, however, it does have a tendency to screw me, by giving me lots of dub(reggae) when I search for dub. Oh well. Now I have many more dub artists in my collection. However, it is truly a useful application. My music library is very small, and also limited to mostly mainstream US music. I start plugging stuff like 'Buena Vista Social Club' and 'King Tubby' and 'Offspring' into MusicLover. It started returning stuff like Bob Marley, Agustus Pablo, and Green Day as primary results respectively.
MusicLover is adware, albeit unobtrusive adware. The only ads it uses are from Amazon.com, and unlike most adware that I've run into, the ads are quiet, and targeted. Since this application is for the express purpose of finding music similar to what you already like, the ads are very small, and extremely targeted. They consist of cover art from two albums, the album names, and an amazon.com icon.
In Short, MusicLover is a nifty little application, not undeserving of praise.
Note: MusicLover is not a substitute for a P2P program. MusicLover is just a tool for the lover of music.
MusicLover can be downloaded from http://www.xlife.org/files/ . MusicLover is free. For now.
UPDATE: MusicLover 0.6 sports several new features.