Twitter button plus is nice and useful tool to show Twitter tweet button on your website.
This plugin allows site owners to reshare their content automatically on a schedule to bring new life to existing posts and increase traffic.
Plugin to share about your old posts on twitter, facebook, linkedin to get more hits for them and keep them alive.
Plugin to Buffer about your old posts to get more hits for them and keep them alive.
Plugin that automatically tweets your old posts (including custom posts) which helps you increase the traffic on your website.
Twitter Widget with Tweet Reach: Shows latest tweets for any keyword or, your handle along with Twitter Reach.