Since everyone will have a different idea of what a button should look like, I think the creativity is best left up to the user. That way our games won't start looking alike.
If you really want to make nice looking buttons to export to PNG, JPG, or GIF format, try
Crystal Button. The quality is awesome and it's very easy to use and churn out as many buttons as you want.
Take a look at some of the examples here:
http://www.crystalbutton.com/examples.shtml