brehash

This plugin adds the official <a href="http://blog.twitter.com/2010/08/pushing-our-tweet-button.html" rel="nofollow ugc">Tweet Button</a> from Twitter to your Pages, Posts or Home Page. It lets your users share links directly from the page they’re on. When they click on the Tweet Button, a Tweet box will appear pre-populated with a shortened link that points to the item that they’re sharing.
This plugin is very customizable via ‘rsh-Tweet Button’ under the ‘Settings’ menu in WordPress Admin. Change the look and feel, pozition and where to seen of the button.

rsh-Tweet

Adds the official Tweet Button from Twitter.com.

riponshah

Social button is a simple plugin for showing your social profile button in any page, post or widget. You can use it by it’s 3 different sizes.
Features: 
1) Support on post, page and widget 
2) very light weight. 
3) Nice design 
4) Easy to embed. 
5) Many icons available. 
6) 3 diffrent sizes avilable.

Social button

This is fantastic

Social button is a simple plugin for showing your social profile button in any page, post or widget. You can use it by it's 3 different sizes.

rsh-Tweet vs Social button