Below are a number of background textures from various sources. With a good paint program, you can create your own images, or alter existing ones:
It's generally a good idea to use simple patterns for backgrounds that don't interfere with the text of the page. Most (but not all) people use black text on a white or grey background, so if you can't read the page with black text, odds are noone else will be able to either.
It is possible to change the text color to make it more readable with the background, but some people get rather militant when you do this. The following HTML 3.0 <BODY> attributes allow you to alter text color: