One of the most popular ways to view multiple social networks from one site is Hootsuite. Although principally intended for use by organizations, it can be useful for individuals. Users can connect streams from various social networks including Facebook, Twitter, LinkedIn, Google+ and Instagram. They can then view recent updates on those streams as well as send out posts to multiple networks. Hootsuite comes complete with analytics tools for gaining insight into social media.
Another popular tool is Tweetdeck. This began as an enhanced interface for Twitter but now supports other social networks, including Facebook and LinkedIn. It is a very flexible platform that aggregates social networks, allows filtering of posts, and provides insight into recent trends. Tweetdeck is available for PC, Linux, Mac and iOS. Compared to Hootsuite, Tweetdeck is more focused on use by individuals.
Netvibes is a web-based dashboard for managing social media including Facebook and Twitter. It is easily personalized to the user's preference. Beyond social networks, it can also connect with RSS feeds, blogs, email and other content streams. Users can also publish content using what you see if what you get design tools. Netvibes is less focused on social networks than the other two services; instead, it is intended to be a personalized front page to the Internet.