Facebook Facebook is the big daddy of social networks, and the app keeps getting better. You can do a lot with it, including uploading photos, chatting and checking your newsfeed. I can also manage all my pages from here.
Twitter Love, love, love Twitter! Actually like the app a little bit more than the web interface, mostly because I have the option of quoting or RT'ing instead of just RT'ing without being able to leave comments.
LinkedIn LinkedIn has come a long way in the app world. When it started it was frankly awful, but now you can do many of the same things as on the web, including easily replying to messages. I don't use this app as much as the others but it works well when I do.
Instagram Now my meals can be shown off to my network in proper fashion... Seriously though, this is an addictive app. Easy to use, photos look great and with one click you can share to FB and Twitter.
Google+ While a lot of folks still aren't getting on board Google+, I actually really like it. The photo sharing aspect on the app is terrific, and I also love huddle feature.