I had a pretty hard time finding the UA for the new Kindle 3. For everyone else's convenience, ill post it here.
Kindle 3 User Agent:
Mozilla/5.0 (Linux; U; en-US) AppleWebKit/528.5+ (KHTML, like Gecko, Safari/538.5+) Version/4.0 Kindle/3.0 (screen 600x800; rotate)
Hope this is helpful to someone.