There just had to be one.
KOTOKO is an artist comissioned quite a lot by ero-game companies, visual novel companies, and anime style companies in General. Some people may recognize her for doing 'Shooting Star' for Onegai Teacher, or perhaps 'Agony' and 'Re-Sublimity' from Kannazuki no Miko. Heck, maybe you'll even know that she Did 'Mighty Heart' for Tsuyo Kiss and "Went Away' for Hourglass of Summer. She actually has a pretty big index of songs.
Her company, publisher, or whatever is called I've Sound. You'll probably see the name a lot if you're into eroges.
I've Sound HP:
http://www.ivesound.jp/ WARNING: the links in this site may get you to some adult websites.There are a number of links in the Music Data section where you will be redirected to company HPs. Many of theese places will have free downloads if you look hard enough. Although I can save you the trouble as I post the links to the downloads myself... as long as the site is PG-13 that is.
*Subject to update