Here is a Twitter background I made a while back that I forgot to post. Green on a black background. Image dimensions are 1263x800px. If I still have the PSD I will add it.
Here is a basic grunge background. Image dimensions are 1600X800px. Took about 10mins to build, PSD included. I started with a center content area size of 960px wide. If you have PhotoShop then you can edit this to fit your needs.