Some really good custom backgrounds for twitter and facebook graphics, While many are paid versions, there is also a section for free twitter backgrounds.
Their site says “Twitter Backgrounds Gallery is the largest showcase of unique Twitter backgrounds submitted and recommended by Twitter users worldwide.” 1644+ free backgrounds, also don’t miss the resources, top10 and other useful sections
Professional looking site, with free backgrounds arranged using tags and categories.
They have a lot of graphics that can be used as background wallpapers for your twitter, especially interesting is their Twitter Logo Section.
Lots of quality stuff here, has an automatic install tool for installing the custom background. unfortunately the manual install doesn’t seem to work.
Simple and clean free templates for twitter.