How can you procure these fetching bat-mods? Initially by preordering at different retailers, though they will all be added as DLC later. Here is where you can get them, according to ArkhamCity.co.uk:
From left to right:
Batman Beyond - Preorder from Gamestop.co.uk or MightyApe
The Dark Knight Returns - Purchase the Limited Edition of Arkham City at any vendor
Batman Earth One - Purchase from MightyApe
Batman 70s - Preorder from ToysRUs
Batman Animated Series - Purchase from MightyApe
(not pictured) Robin's Red Robin skin - Purchase from Best Buy
MightyApe is a store based in New Zealand, and there's no word yet on if those skins will be available at launch to US residents.