I'm a fairly new Blender user, and I'm doing pretty well, but I am having trouble with making realistic textures for my meshes. Can anybody refer me to a good (preferrably free) textbook or tutorial on how to make textures in Blender, or perhaps have any good tips they'd be willing to share?

(please note: I like blender, and I do not wish to use another program, so please don't try to recomend one)

Thanks in advance!