The Spriters Resource. Sprite Database. Game Art Tricks.
Animation-stock (Animation stock images) on deviantART. OpenGameArt.org. Esoteric Software. Textures. 3D. IconWorkshop - Make icons for Windows, Mac, iPhone, Android, Windows Phone. One professional tool for all your needs IconWorkshop™ is a professional tool designed to Create, Extract, Convert, Manage and Redistribute Icons.
You create professional looking icons. You work like a pro, you're seen as a pro.
GIMP - The GNU Image Manipulation Program. Inkscape. Draw Freely. Welcome to OpenGameArt.org. 2D Game Art for Programmers. Color Theory And Color Palette Editors.