When choosing a background for your website you have many choices. You can select to just show a plain background with some color in it or you can choose some background image. Sometimes I use vertical gradients as a background on my sites. The gradient color matches the color theme of the website in whole. On other hand sometimes I just go for some stripes and tiles stuff. Which when given a repeat property in CSS would look good. In the stripes and tiles case I go for contrast rather then the blending effect.
I would even suggest that on some niches or the websites even Wallpapers can be used to make a background for your site. EX: I did had a cookery site that I was given by one of my friend to do some touchups. Its menu, design and the flow was fixed and I also added a nice wallpaper as its background and the site just came alive. Just make sure that the size of the wallpaper that you use is quite good enough to fit on high resolution monitors.
Moreover one more thing to keep in mind is check out the usage and copyrights for the wallpapers. You can choose anonymous wallpaper from sites offering them and give proper credit if it is necessary. Just make sure that you read the terms and conditions on the wallpaper site about its usage policy.
I hope this tip will help in designing or re-designing the websites of yours.