I recently launched a simple charting plugin for WordPress called RJ Quickcharts. During the process I needed to figure out how to add a banner image. The process is really simple but I thought it would have been nice to have a template that was the right dimensions and had the title of the plugin in the right area.
The zip contains 2 files: a 772x250px PSD and a 1544x500px PSD for hi-dpi screens. To use them, simply create your image and save the files as “banner-772×250.png” or “banner-1544×500.png”. The PSD’s already use this nomenclature so you should be able to simply “Save as…” -> PNG. Once saved, move them to your /assets folder in your SVN repo.
Some links I found helpful while getting these images set up.