I’ve been using Twitterfeed to auto-post from here to Twitter. Unforunately it’s now doing sporadic updates and seems unreliable.
However, you can use Google Feedburner to auto-post from your RSS feed to Twitter. Choose the feed, Publicize / Socialize.
Added bonus: Configure your blog to use PubSubHubbub (WordPress has a plugin) and the Twitter update will be near-instantaneous, like within seconds. Sweet.