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.
I think twitterfeed is a victim of it’s own success, the high volume of posts it pushes to twitter must effect it’s bandwidth as well as it’s whitelisting status (the way we apps like twitterfeed can post more than 150 tweets per hour)