Alchemy is a free open drawing program that encourages creativity and rapid prototyping. In fact, alchemy is not designed for creating final artwork, but rather a space where an artist can sketch and experiment. Alchemy features brushes that can use procedural shapes to help give the artist new ideas. There is also an interesting feature that allows a user to mirror their canvas and work on a symmetrical image. A lot of content can be generated randomly which hopefully can lead to ideas in the initial concept stage.

xNormal is a great tool for baking normal maps based on higher resolution geometry. An artist can freely sculpt high resolution characters with the knowledge that all their detail can be captured in a great normal map generated by xNormal. The workflow is simple. Import your high resolution mesh and a low resolution mesh with UV's laid out. It can then bake a normal map that corresponds to the UV's on the low resolution object. From what we've seen, xNormal seems to be the fastest , most stable and most robust tool for this type of baking. As well as normal maps, you can bake Ambient Occlusion Maps, Height Maps,
and several others.

Gimp is free image editing software that runs on Windows Mac and Linux. Although those who maintain Gimp claim that it is not designed as a Photoshop replacement, there are many features in Gimp that are comparable to Photoshop. Some of these features include image editing with brushes, layer control and selection tools similar to those in Photoshop. There is also a large library of filters and effects as well as scripting support.

CGTextures is a gold mine if you are looking for free high quality textures. Although they offer a paid membership with even higher quality textures, their free content is a great resource for any game developer. One of the most desirable features of these textures is that many of them tile. Even textures that seem random and complex still manage to tile perfectly. These textures are royalty free and as long as you are not reselling them, you are free to use them in your game. The textures also go beyond the standard brick, concrete, grass or other simple materials. Many of the textures are of complex ornamental designs or architectural elements that can even be used for modeling reference.