Batman Arkham City (Download Code by email) - $14.99 - Xbox 360 - Ozgameshop
Batman Arkham City is a must play game IMO, and is just as good if not better than the original in the series, Batman Arkham Asylum.
It was Metacritic's 2011 Game of the Year, and it won a stack of other awards:
For those who prefer a physical copy, EzyDVD and Blockbuster have UK copies for ~ $21 delivered atm...would likely be 2 - 3 weeks wait for delivery though.
Bring on Batman Arkham Origins in October 2013!