As promised back in September, DC Universe Online is now free to play. While the combat isn't quite as smooth as Mr Wayne's moves in his Arkham adventures, it's a lot more punchy than what passes for fisticuffs in most massively multiplayer efforts. Playing for free only provides two character slots and there are limits on inventory size among other things, including an inability to trade. You can see all the difference between paid and free subscription at the site.
I'd say it's well worth a look for anyone interested in the characters and world, and it's an entertaining solo game for a while if nothing else. I'm hoping this helps to repopulate Gotham since DCUO is the only online RPG I actually play. It's lonely in there with no one to watch me brooding in the shadows. Get it here.