Tweet Old Post Widget

Tweet Old Posts is a plugin designed to tweet your older posts to get more traffic to them.

Tweet Old Posts randomly picks your older post based on the interval specified by you. The primary function of this plugin is to promote older blog posts by tweeting about them and getting more traffic. This helps bring "back to life" some of your older tweets by sprinkling them in with your newer ones.

Link: http://wordpress.org/extend/plugins/tweet-old-post/