I sometimes use those backgrounds, but your request is perhaps a little too generalized to be able to give you a simple reply. What I also do is use those backgrounds in my image editor to make something a little more complex - it doesn't take much. So much depends on what kind of site you need an image for, and often the imagination comes in with the use of other small graphics to combine with the background.
As David says - sometimes having one image on top of another is very effective, just keeping the top layer pinned up at the top of the background area as a single image, whilst the main background image is tiled to cover.
Here is an example:
http://www.vallejoviolinlessons.com/
The dark red "brocade" is used to tile the whole area, but I have pinned a small transparent "musical" background image up top left of the content area.
Have you got a particular site to build? Maybe we can offer some specific suggestions. Meanwhile feel free to see the kind of thing I do with backgrounds on my blog...and of course do download any that might be of interest to you.
http://trashyourblog.blogspot.com/search/label/blog%20background