Some neat respnses here that got me thinking of things other than soundtracks that might motivate me.
Agree that a physical soundtrack is what I want. That said, I have never seen an offering for just a soundtrack download code.
Money off is a fantastic motivator, I agree, I also want to buy digitally more these days, so I would love to see a digital pre-order program on Wii U that got you a discount. I already have the Deluxe Promotion, but that is not a pre-order incentive since (for now) I can use it whenever. Plus, it is not actual money off the price.
Free DLC in the form of extra playable content (not just maps or costumes or weapons) is a decent motivator provided I know what it is ahead of time. I am not a fan of the season pass idea where you will get all the DLC as it comes out for what ends up being a discount. What if I don't give a crap about the DLC? Too late, I bought it. I pre-ordered Batman Arkham City for the free Catwoman playable scenarios. In retrospect (as I still have not completed that game) I probably would have been better off (financially) waiting for the Wii U version. But then again, it would have been torture for mee to not be able to delve into Gotham every now and then over the past year. Love that game.