twitterfeed is a great, useful, and free service that allows you to feed your blog to twitter, or more generally speaking to post RSS to twitter automatically.
Basically, you add feeds to twitterfeed, it checks them periodically for new items, and posts tweets when it find some. Settings allows you to tell it how often to check, and how to format the tweets.
It also support identi.ca and ping.fm.
And you can extend the concept by adding non-blog feeds such a your photostream feed on Flickr, your bookmarks feed on del.icio.us, your Facebook status feed, and the likes, so that your followers may be notified of your activities on the social web...
See my profile for examples :
@poligraf
Hope it helps !