Hey

well as there are sheet music for all the popular games **cough final fantasy cough cough** I would like to know if anyone knew where I could find the piano sheet music for other games that aren't as popular as Final Fantasy e.g. Wild Arms or Shadow Heart series

feel free to give link to other game series as well

Have you visited Ninsheetmusic.net (http://www.ninsheetmusic.net/) yet? They've got plenty of video game related sheet music, mainly from Nintendo's genre but recently there have been added some other titles too, Halo and Kingdom Hearts for instance.
The other site I'd recommend is Gamingforce Video Game Sheet music (http://www.gamingforce.org/forums/musicians-library/44-video-game-sheet-music.html) thread, albeit most of the sheets are from Final Fantasy series.