Facebook – the largest social media/networking site in the world
MySpace – the original social media/networking site geared towards musicians, group, bands
Twitter – the most popular microblogging social network in the world.
Digg – a popular social news service where users rate article/stories across a variety of industries and categories.
Yahoo! Meme – a microblogging platform owned and run by Yahoo! Inc.
Google Buzz – a social networking system designed and owned by Google Inc that integrates with their Gmail product.
Delicious – a social bookmarking service that allows users to share, store and find articles/news/stories.
StumbleUpon – a social publication service of news, photos, links, videos, articles and user generated content.
Bebo – a social media / networking website owned by AOL
Foursquare – a mobile Geo-location social networking service
Gowalla – a location-based social networking service.
Flickr – is a popular picture, image and video hosting website owned by Yahoo! Inc
Technorati – a search engine for blogs and social content.
Reddit – a social news aggregation service.
FriendFeed – a real-time social media aggregator
LinkedIn – is the largest professional social networking site in the world for businesses and business people.
Tumblr – is a microblogging service that allows users to post text, images, videos, links and other web related content.