Decoupled from socialy-networky things, the Hearthstone Deck Tracker is a straightforward tool to use (after a bit of fiddling at the start). It’s available for Windows and Mac so go get it.
Hearthstone Deck Tracker
There are plenty of plugins to choose from, too. My only hard recommendation is Hearthstone Replays, which has made it possible to study my games and figure out where everything went horribly wrong.