Batman: Arkham City - Game of the Year Edition includes the following DLC:

Catwoman Pack
Nightwing Bundle Pack
Robin Bundle Pack
Harley Quinn’s Revenge
Challenge Map Pack
Arkham City Skins Pack

Batman: Arkham City - Game of the Year Edition packages new gameplay content, seven maps, three playable characters, and 12 skins beyond the original retail release:

Maps: Wayne Manor, Main Hall, Freight Train, Black Mask, The Joker's Carnival, Iceberg Long, and Batcave
Playable Characters: Catwoman, Robin and Nightwing
Skins: 1970s Batsuit, Year One Batman, The Dark Knight Returns, Earth One Batman, Batman Beyond Batman, Animated Batman, Sinestro Corps Batman, Long Halloween Catwoman, Animated Catwoman, Animated Robin, Red Robin and Animated Nightwing