Auto Tweet is a plugin to cross-post selected entries to Twitter.
Auto Tweet adds a check box to the Write Post editor (both the TinyMCE/Visual Editor and the advanced editor). When this box is checked, publishing your post will also send the post to Twitter. If a post is longer than 140 characters, it will be truncated. Auto Tweet creates a new column in the "posts" table of your database to mark which posts have already been submitted and will use that information to help prevent double-posting.