One of the best free design resources online is, in my not-so-humble opinion Media Militia. Media Militia gives away tons of brushes and texture packs, and adds in tutorials on how to use all those materials.
Check out the posts like this collection of inspirational design or tutorial for vivid lighting illustration on Photoshop. Maybe you find interesting this article about getting rid of that monster called Creative Block. Pretty nice, isn't it? One improvement suggestion I do have: Please include GIMP tutorials.
For more inspiration, check The site of Tuesday collection.