I looked for a plugin to add tweet button to my wordpress blog. My main problem was that even when I added plain official twitter button, I couldn't tweet posts from my homepage (the excerpt ones), it used homepage url but not post url. The plugin solved this problem and even lets to choose that the button will be displayed on the top and the bottom of single post and page, but only on the top when the posts are listed on homepage — which was exactly as I wanted!
Also lets choose what info to put in tweet, button language, url shortener, etc.
Very useful, thank you!