Brid.gy has a cool feature for automatically posting blog posts to Twitter, which is interesting because it uses Webmentions to kick off the whole process. I.e. just including the link:

<a href="https://brid.gy/publish/twitter"></a>

The webmention sent to brig.gy triggers it to look back at the post, parse it and look for microformats indicating what content to publish, and then posts it to Twitter.

Using webmentions to trigger brid.gy to publish to Twitter

Note that this also works for Facebook and Flickr, and you obviously need to authorize brid.gy to post to Twitter for you.