InfoMogul’s Social Media Guide contains a more detailed version of this post.
Types of Sites
Profile / Real Life Network Sites
Facebook – photo sharing with friends, messaging, best network
LinkedIn – professional network, jobs
MySpace – more customizable than Facebook, ability to share more info
Micro blogging
Twitter – link sharing, web activity log
Mini Blogging
Tumblr – simplified, concise blogging, very easy to look at and scroll through, yet no sidebar or tags / labels
Blogging
WordPress – best blogging platform, most templates, best look, a bit more advanced than blogger, can install easily on custom domain
Blogger (blogspot) – most customizable layouts, can move “gadgets” or widgets around with ease, feeds and blogrolls look nice easily
Information Consolidation
Plaxo – next gen Facebook, “auto twitters” all of your online activity (facebook, bookmarking, flickr uploads, blog posts, etc.)
Delicious autoblog – this is a daily autopost of any bookmarks you add to delicious
Multiply – allows you to import specific posts from any of your blogs
Information Syndication (Simultaneous Publishing)
Posterous – post all your posts here, then you can select which blogs to syndicate the given content with only two clicks, great bookmarklet tool to grab content with, just looks nice without any effort, best blogging platform, but not meant for viewing since limited theme selection
Ping.fm – cool for updating your networks probably, might be obsolete because of posterous
Content Sharing (General/All Purpose, Bookmarks, Books, Songs, Videos, Pics, Websites, Articles)
Digg – links, to mostly articles and videos, good for pages as opposed to entire websites
StumbleUpon – websites as opposed to pages
Diigo – bookmarks, comments anywhere, highlighting important page content
Goodreads – books
Soundcloud – song sharing, this may be my new favorite
Blip.fm – song sharing, allows you to “DJ your own radio station”
Last.fm – music discovery
Youtube – videos you create
Vimeo – like youtube, but better because it allows longer videos than 10min
Flickr – artistic photos, good networking
PicasaWeb – personal / family pictures