Check out these sites, and download some of the textures they offer, generally for free.
Deviant Art – Unique and unusual textures and so much more, often made by the users so you can find stuff that is really different.
Amazing Textures – Not completely free. Access to samples etc, but subscription for full library.
Grunge Textures – Small files 900×600 are free, anything above is either $2 or $3, good selection of textures.
Shizoo – A more unusual selection, with some cool textures, they also have brushes, icons patterns and materials.
CG Textures has a huge range of tiles and textures, of varying size. Really useful.
I stumbled across these gradients (for use in photoshop), again useful for your architectural visuals, great for overlays when you are trying to create atmospheric effects on your CGIs.
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