Buttonmakerjs is a project mainly written in JavaScript, it's free.
A simple tool for generating CSS buttons.
A simple tool, written in javascript to generate CSS (and an image sprite for old browers) to create cross-browser buttons for use with button and a elements.
The generated code also contains a comment with javascript to restore the values that you used to generate your buttons. This way you can easily revisit a design without having to add back every color and also benefit from any future improvements/bug fixes in ButtonMakerJS.