Full disclosure: the author is a friend of mine. To use the service as a merchant you need a Google account. I believe the system only works for customers who have JavaScript enabled.
http://www.reddit.com/r/Bitcoin/comments/ibfxf/my_weekend_project_accept_bitcoin_on_your_website/
http://bitwillet.com/
I just saw this on Hacker News. I have a site going live shortly and this is exactly what I needed...anyone know if it is safe or if there is a better alternative.
Haven't gotten a chance to test BitWillet out, but MyBitcoin has a secure shopping cart interface that is heavily adopted already.