Thought that this was interesting: http://css3buttons.michaelhenriksen.dk/
Author states that IE8 or earlier has problems, but it fails gracefully back to IE6. Definitely makes it usable in my mind.
Nice!
I tried it in IE8 and the only thing that doesn't work is rounded corners. There are some fairly simple and robust solutions to getting rounded corners in IE, so I bet someone will commit that to git and it will be 100% cross-browser.