If you are in the US, then the GOTY version comes out tomorrow, which is the game, every bit of DLC including "Harley Quinn's Revenge" due out tomorrow, and a free digital download copy of the animated movie Batman: Year One (great animated Batman Story)
If you are outside the US, then the GOTY is not out until September. If you get a new copy of the game, then you get the Catwoman DLC as standard. If you enjoy the combat and the challenge maps from ayslum or are just a fan of the Batman universe, then
the DLC packs of Robin and Nigtwing are a must, so much fun using the different combat style of each character, Batman, Catwoman, Robin and Nightwing.
The Harley Quinn DLC is the first and only Story driven DLC the game has, totally SP and over 2 hours long
A New copy of the game in the UK will cost £20-25 if that, a 2100 points card will get you ALL the DLC bar the skin pack which is only 400MSP