By our count, there are 14 alternate costumes or characters you may play as in Batman: Arkham City, through a variety of promotions, pre-order bonuses, and timed-exclusive downloadable content available now. The "good" news, I suppose, is that all of this stuff will be available at some point—for a price.
So if you're intent on collecting Batman's entire wardrobe, don't run out and buy the NOS energy drink, the Green Lantern DVD, and two copies of the game, one from Best Buy and the other from GameStop. Unless, of course, you really want to.
Of course, the bad news is that all of this stuff will be available—at a price. Specifically, $7 gets you Nightwing on Nov. 1, and another $7 gets you Robin's DLC on Nov. 22, and finally $5 will get you the Skins Pack, which is all of Batman's costumes, on Dec. 6. The Catwoman DLC is included with new copies of the game, and GameStop is even giving out Catwoman DLC codes for used copies. Otherwise it's $10, sort of like an online pass.
There was also a pre-order bonus that did not include any skins. The Joker's Carnival, a challenge map, was offered by GameStop (U.S.) and Tesco (U.K.) No word on its availability otherwise. The Iceberg Lounge challenge map was included in the $99 Collector's Edition. No word on its future availability.
One final note: All alternate costumes are available after beating the game once. So if you're waiting on that first DLC drop, be sure to finish up the main campaign.
Alright, I've rambled enough. Here's a look at the many looks of Batman: Arkham City. Unless otherwise noted, all purchasing information is U.S. based.
How to get it: Buy a can of NOS energy drink. Under the tab (or cap) there's a code. Plug that into this website and you'll get another code. Plug that code into PSN or Xbox Live and you get the skin.
The Dark Knight Returns
How to get it: It comes with the Arkham City Collector's Edition.
Earth One Batman
How to get it: So far available only in Australia or New Zealand; purchase the game from either Mighty Ape (New Zealand) or JB Hi-Fi (Australia)
How to get it: Came with a preorder of the game at Toys 'R' Us.
Batman: The Animated Series
How to get it: Be a member of GameStop's PowerUp Rewards club, buy the game from GameStop.
Batman: Year One
How to get it: Available in the $5 Skins Pack on Dec. 6.
Sinestro Corps Batman
How to get it: PS3-only so far. Buy the Green Lantern Extended Cut Blu Ray. It's got the code for the skin inside. It will become available in the $5 Skins Pack on Dec. 6.
All skins shown will be available in the $5 Skins Pack on Dec. 6.
Catwoman (standard), Catwoman (The Animated Series) and Catwoman (The Long Halloween)
How to get them: Buy the game new. Basically, it's another $10 "Online Pass", but GameStop is giving out codes free to those who buy the game used. The Catwoman DLC also includes a substantial chunk of extra content, including extra missions and Catwoman-specific Riddler trophies to collect.
Red Robin, Robin and Robin (The Animated Series)
How to get them: Buy the game from Best Buy. Like Catwoman, this comes with extra content playable only as Robin. The DLC also will be available for $7 on both networks on Nov. 22.
How to get it: Available Nov. 1 as premium DLC for $7. Includes extra playable content.