Social bookmarking is a method for Internet users to store, organize, search, and manage bookmarks of web pages on the Internet with the help of metadata. In a social bookmarking system, users save links to web pages that they want to remember and/or share. These bookmarks are usually public, and can be saved privately, shared only with specified people or groups, shared only inside certain networks, or another combination of public and private domains. The allowed people can usually view these bookmarks chronologically, by category or tags, or via a search engine.

• addThis button spreads your content across the Web by making it easier for your visitors to bookmark and share it with other people, repeatedly. AddThis helps your visitors create a buzz for your site and increase its link popularity and ranking.

• addtoany is a popular sharing button widget provider. Some of its feature includes tabbed menu, Real-time Digg counts , Real-time Delicious
  counts, E-mail made faster/easier, Prioritize services, In-widget browser bookmarking instructions (for non-IE browsers) and more publisher options.

• ShareThis believes that sharing should be simple and lets your readers instantly access all of their profiles, blogs, friends, and contacts easy sharing and updating.

• Tell a friend adds support for social bookmarking on 15 popular sites like; Digg, Delicious, StumbleUpon, and Yahoo Buzz to its already impressive support of email, IM (chat), blogs, and social networks. Tell-a-Friend button is now the single powerful tool for social referrals with both one-to-one messaging and one-to-many broadcasting across social sites. Tell-a-Friend has clearly been made to be the standard bearer of social web share tools, becoming first brandable and customizable social share button.