Whether you are rendering crumbling ruins of ancient Cambodian temples or the smooth marble dome of the Taj Mahal in India, texture files can be an invaluable resource for visual creatives. Lately I've been developing a texture library, and I'll be sharing that in the upcoming months. In the mean time, here are some free concrete, stone/brick and wood textures compliments of Disney character designer Chris Oatley (thanks Chris). Also be sure to check out his very informative and somewhat humorous article: The Hudson River Painters Vs. The Texture Monster: Digital Painting Tutorial.
A couple other great texture resources for print and web I've also found useful are Texturly, Lost & Taken and Mayang's Free Texture Library. Happy hunting!