Twitter's apparently decided to get in on that action themselves with official buttons, and Mashable's got the confidential document's to prove it. In the slideshow (part of which you see above) the full, simple string of code for the buttons seems to be revealed, as well as their three relatively innocuous and somewhat predictable designs. We've got a feeling you'll be seeing these absolutely everywhere any day now, but hit the source link to see the full deck of slides.
Update: Well, that was quick -- Twitter's dropped the official buttons, and announced a partnership with TweetMeme at the same time. You can see the buttons in action on this post right now, and hit up the Coverage link for the official announcement of Twitter's blog.