Today I stumbled upon an excellent collection of textures. They're free, no need to register, all seamlessly tileable.
Navigation of the site isn't very easy; part of it is organised as a blog. Have a good look and you will find a wealth of textures.

There is also a very nice collection of high quality Sketchup models with textures that (using SKetchup) can be easily converted to DAE models for SH3D.

Hans

EDIT
Oops, I forgot the link: http://www.sketchuptexture.com/