ASP .NET
PHP

Twitter backgrounds need to look good across all screen resolutions, if you view a twitter page in a computer screen with a resoltion 1024×768 it can look alot different than id seen on a larger screen of say 1920×1200. For that reason making cross rez twitter backgrounds is useful...so the design has to take that into account. The following background image, shows how at different res, the Twitter box in the center will cover certain parts, leaving the rest of the design around the edges looking clean


1280 by 768
Useful photoshop template using masks can be downloaded here