This follows on from a blog post I wrote recently about the WordPress Welcome Email Editor. I have released the plugin into the WordPress Extend Directory. This page is used to host a changelog and screenshots.
As there were no hooks for the welcome email I had to override the wp_new_user_notification function and write my own then simply converted it to use Options and wrote a nice admin page for it. Let me know if I can extend it at all or if you find any bugs..
Downloads have been moved to the WordPress Plugin Directory although you can download the first version below.