Seriously, if you have only watched the 2 seasons of the anime, do yourself a favor and read the manga. From the looks of it, whether there will be a season 3 depends on how well the upcoming OVA does, and that’s never a good sign, so now would be a great time to start reading. Son, you won’t be disappoint.
If you decide to pick up the manga, then I suggest you hop on over to RedHawkScans and start from Chapter 42 if you watched through to the end of Season 2. If you haven’t watched the anime OR read the manga, THEN WHAT ARE YOU DOING? GO READ THIS FROM THE BEGINNING NOW.