Game Content Resources

Bitmap

 * pixeljoint.com - Very useful pixelart/sprite website.
 * Deviantart pixelart area - The pixelart areas of Deviantart.com.
 * eboy.com - Cool pixelart site with many different pixel artworks.
 * GFXZone 8bit Gallery - A gallery with many 8bit demoscene images.
 * Game Making Resources - A complete index of the GMC.

3D

 * Tronitec Game Studios - Low polygon 3D game models (commercial).
 * Turbosquid - Free & commercial 3D models.
 * The3DStudio - Free & commercial 3D models.

Fonts

 * Game Making Resources - A complete index of the GMC.

Textures

 * mayang.com - Mayang's Free Textures, great source of free high-res textures. Users can download 20 hi-res textures per day.
 * spiralgraphics.biz - Tons of free textures, all fully seamless.
 * texturebin.com - New texture site with tons of medium resolution textures, many of them quite original.
 * imageafter.com - Another nice texture resource with tons of free high-res textures.
 * textures.z7server.com - Textures Library, for free use.
 * Game Making Resources - A complete index of the GMC.
 * Tronitec Game Studios - Quality seamless game textures in multiple resolutions (commercial).
 * Turbosquid - Free & commercial textures.
 * The3DStudio - Free & commercial textures.

GUI (Graphical User Interface)

 * Tronitec Game Studios - Game gui elements (commercial).