addthis.com have a great free social networking bookmark tool. They provide a single piece of JavaScript code, which you can add to your website. The JavaScript displays a pretty image which visitors to your website click. The visitor is taken to the addthis.com site from where one can chose which social network to submit too. There is a beta version of the JavaScript widget which which allows a drop down of the various social network sites. All the major social networking sites are available.

Social networks a great way of gaining backlinks and traffic to your website.