Sounds and Music

• Kevin MacLeod – Hundreds of music tracks in a wide range of genres (CC-BY)
• Freesound – Lots of creative commons sound effects and music.
• OpenGameArt.com – Art, music, and models. Under a vareity of licenses, so pay attention.
• Green Island soundtrack by Alpha Secret Base

Images and artwork

• CC Search – Search several media and image sites for creative commons content.
• OpenGameArt.com – Art, music, and models. Under a vareity of licenses, so pay attention.

Fonts

• Font Squirrel – Lots of awesome fonts with a free commercial licenses.

Random stuff

• Alpha Secret Base (Japanese only) – Games, music, art, etc… The content is under a BSD license according to this notice unless a more specific license is included on a page / in a file.