There's another date formatting library if you're using Prototype, that I've used for a few things (although I have to say, I like the OP better). It was kind of hard to track down and doesn't seem to have any continuing support, but is used as part of this nice date picker:

http://home.jongsma.org/software/js/datepicker

This is the .js file:

http://home.jongsma.org/js/lib/prototype-date-extensions.js