"The Mudcat Labs network" section is populated with with the same things that the Handmade Magic Search (the Google Custom Search blank below the regular mudcat search) is made from, a list of 50 sites hand-picked by me that contain great data like mudcat. They include but not limited to:

http://dev.mudcat.org/
http://www.thebards.net/music/
http://maxhunter.missouristate.edu/
http://folkmusic.about.com/
http://www.thesession.org/
http://www.camscomusic.com/
http://www.csufresno.edu/folklore/ballads/
http://www.froots.net/phpBB2/
http://www.traditionalmusic.co.uk/
http://www.folktunefinder.com/
http://itu.se/eirinn/ceol/g/
http://www.hymnsite.com/
http://www.fasola.org/indexes/
http://www.ceolas.org/
http://www.contemplator.com/
http://www.folklib.net/
http://memory.loc.gov/ammem/mussmhtml/
http://www.mun.ca/folklore/leach/
http://www.cowboysong.com/
http://www.harptab.com/

So it should be real good data.

Also, the Amazon links are tagged with our affiliateID so we'll get a cut of any sales that their inclusion may lead to.