Wikipedia
ShareThis
The ShareThis button is an all-in-one widget that lets people share any content on the Web with friends via e-mail, AIM, or text message. Shar.es is the URL shortener for ShareThis.com. The widget can also keep an account of personal contacts so that users can send an e-mail, IM, or text message with favorite links to friends. Toolbar versions exist for Firefox, Mozilla Application Suite and Internet Explorer, and customized widgets are available for leading blog publisher sites including Blogger, TypePad and WordPress.