FX

Images

• Lost Garden has lots of tiles and other video game imagery. (highly recommended)
• Photos licensed under Creative Commons at Flickr
• Tons of cool shapes and vector artwork
• Free textures and vector shapes. Good for backgrounds and skinning

Color Schemes

• COLOURlovers: Color Trends + Palettes

Fonts: Specifically look for fonts that are free to use

• Larabie Fonts
• 1001 Fonts .com

Sound Effects & Music

• The Freesound Project
• ArtistServer.com: Music Genres : Progressive Electronica
• Togeo Music

Icons

• Icon sets for Gnome, under various licenses
• Oxygen KDE Icons. A very complete set of desktop icons for many uses.
• Tango KDE & Gnome icons: another very complete set of desktop icons.
  • Tango Desktop Project
  • Tango Icon Library

Creative Commons

A copyright license which allows various forms of use on some copyrighted works (particular rights vary by the work being licensed). Rights include the ability to create derivative works. Their site has links to many other sites with Creative Commons licensed content. » More info