1. Wickett Twitter Widget:

Wickett Twitter Widget can display tweets from a Twitter account in the sidebar of your blog. Example can be seen at WordPress.com, it has easy to use interface, so it is easy to set your own settings.

You can get Wickett Twitter Widget Plugin from here

2.  TweetMeme button:

TweetMeme button – The TweetMeme retweet button easily allows your blog to be retweeted. The button also provides a current count of how many times your story has been retweeted throughout twitter. Tweetmeme, owing to it’s analytics (you can view the analytics for the last 5 posts) has become the default ‘Tweet this’ plugin for blogs and we strongly recommend you to use this for your blog. The plugin is easy to configure (right from button placement to choice of URL shortener as well as source name).

You can get TweetMeme button Form here

3: TweetBacks:

TweetBacks for WordPress – People are talking about your posts, and not only in the comments of your post. A lot of that conversation is happening on Twitter, and now, you can take that conversation right back to your blog! This plugin imports those tweets about your posts as comments. You can display them in between the other comments on your blog, or display them separately.

You can get TweetBacks plugin form here

4. The Twitter Updater:

The Twitter Updater is a WordPress plugin that automatically sends a Twitter status update to your Twitter account when you create, publish, or edit your WordPress post. You can specify the text for the updates, and also have the option to turn the auto update on/off for the different post actions in the admin panel.

You can get The Twitter Updater from here

5. TwitThis:

Twit this WordPress Plugin Twit this WordPress Plugin provide you an easy way for people to send Twitter messages about your blog post or website. When visitors to your website click on the TwitThis button or link, it takes the URL of the webpage and creates a shorter URL using TinyURL. Then visitors can send this shortened URL and a description of the web page to all of their friends on Twitter.

You can get TwitThis plugin form here