Facebook
The ultimate platform for keeping up with (stalking) friends. I joined Facebook way back in 2005, you know, when it was just for college students and before you could even share photos (gasp!). I’ve witnessed the evolution of this mega-network over the years, and it has become, not only the 4th largest website in the world, but the best place to find people, keep up with them, and inform them. It is the son of Classmates.com on every possible steroid ever ingested by humans. The ability to share and communicate with friends and colleagues is seamless. Overall, Facebook is a great place to start your social networking endeavors.

LinkedIn
A must-have in every business person’s arsenal of tools. If you are (or hoping to be) in business of any sort, LinkedIn is a great place to set up shop. Very similar to Facebook, minus the annoying applications, plus job postings and resumes. This is where you network with those in your industry, join groups, research companies, and prospect clients. Build your credentials by asking colleagues for recommendations or head to the “Q&A” section to offer advice.

Twitter – Share, Learn, Meet
I wouldn’t be surprised if Webster adds a new definition for “tweet” this year. Within the first half of 2009, Twitter has gone from nearly 5 million users to over 23 million. It is the social media platform of choice at Fortune 100 companies. Easily share links, pictures, videos, articles… Oh, and personal updates… with followers. Twitter is kind of like the cocktail party of social networks. Here, you can easily reach out to strangers by tuning in to their tweets or quickly replying to them. A limited amount of customization keeps annoying advertisements and outlandish profiles at bay, unlike the outdated MySpace.

Digg, del.icio.us, StumbleUpon, reddit, etc.
Social Bookmarking to share and store your favorite links. You just read an article over at NYT.com that you loved. Use one or more of these bookmarking sites to share it with the world. Looking for information or articles on a certain subject? Head to one of these sites and search your topic, you’ll be able to peruse a list of articles or sites that others have found useful or interesting. Not only are these great for sharing, but storing sites for later use as well. Say you have a home desktop, a netbook for travel, and a work computer… customize your bookmarks and easily access them on each computer without updating each machine.

FriendFeed
All of your networks in one place. FriendFeed lets you put all of your networks in one big stream. Users can see your Facebook status, latest Tweet, pictures posted on Flickr, blog post, bookmarked article and much more when they follow your feed. Much like Twitter, but a whole lot more.