The most common one I've seen used is tweetmeme. Check out http://tweetmeme.com/about/retweet_button for more details.
-----Original Message----- From: firstname.lastname@example.org [mailto:twitter-development-t...@googlegroups.com] On Behalf Of genshu Sent: Tuesday, August 11, 2009 2:01 AM To: Twitter Development Talk Subject: [twitter-dev] I need a "twitter this" button for my website Hi! My website is www.juststuff.de and I want to add a "twitter this" button on every page, a user has uploaded. Like usually on other networks. Can you help me with this? Before I build my own, I want to use a template which surely exists. Most times you get a standard popup.