If you want me to indicate one name then it should be "Facebook". But if you want me to create a list then the list should be Facebook Twitter Reddit Instagram Google+
I use Facebook, Twitter, Pinterest, G +, Stumbleupon and digg to name a few, I want to start getting other social networks sorted out as well, the more the better. The way I look at it is everybody is different some people may say for an example Twitter doesn't work for them yet others it will. I think half of it is trial and error, keep trying different ones and compare results, dump social media that's getting you nowhere and try replacing it with something that will get you somewhere. Sign up to the lot of them, I'm certainly going to.