Although Twitter have their own retweet system, people still prefer to use ‘RT’ to retweet something interesting. It makes retweeting services still have a lot of users that use retweet button in blog post. I have 3 recommended retweet plugins for WordPress.
Usually retweet plugins are provided by retweet services, so you haven’t to worry because it was developed by trusted team. 
Check them out!
Retweet.com
It’s a free WordPress plugins, you can see the count of how many times your blog post retweeted. URL shortener support and find the most retweeted posts at its website. Available in 2 button sizes.
Topsy
Topsy is different, it has a unique ability to give a trackback/ping to your blog post each time you retweet with Topsy, It has 2 choices of button styles and URL shortener.
Download :
via Wordpress
Tweetmeme
It provides 2 styles of retweet button and has an integrated URL shortener. Integrated Tweetmeme Analytics.View the showcase at Tweetmeme.com.
Download :
via WordPress
It’s up to you, which one do you like? 
Happy retweeting..
