TweetSuite - ReTweet-This buttons for each TweetBack A digg-like Tweet-This Button Automatic Tweeting of new posts A Most-Tweeted Widget A Recently-Tweeted Widget A My-Last-Tweets Widget A My-Favorited-Tweets Widget

Tweet This! - A great plugin that adds a Twitter link to every post and page, so your readers can share your blog entries on their Twitter accounts with ease. Shortens URLs in advance too.

Twitter Badge - Display your latest updates with a customized widget.

Twiiter Tools - Twitter Tools integrates with Twitter by giving you the following functionality:

Archive your Twitter tweets (downloaded every 10 minutes)
Create a blog post from each of your tweets
Create a daily or weekly digest post of your tweets
Create a tweet on Twitter whenever you post in your blog, with a link to the blog post
Post a tweet from your sidebar
Post a tweet from the WP Admin screens
Pass your tweets along to another service (via API hook)

Thread Twitter - Display your tweets in thread style.

Twitter reTweet - This plugin provides a retweet link . Your visitors can retweet your posts.

Twitter Dash - A plugin that adds Twitter to your dashboard.