How to get TDKR soundtrack for free legally
Update: Amazon says "Limit of one promotional credit per order". I wiould interpret that as you can only apply $2 max for a single purchase. Bummer.
Fandango.com has a promotion going on right now. If you buy any movie tickets in the month of July, you get $2 of Amazon MP3 credit. Go watch The Dark Knight Rises 4 times (you are watching it multiple times, aren't you?). If you buy your tickets through fandango, you'll get $8 in credit -- enough to buy the TDKR soundtrack. Make sure you get the deluxe edition which comes with a few extra tracks for the same price. I've done this 3 times, and I've received the $2 credit each time.
The fine print says you will get credit for each ticket purchase transaction. I tried buying 2 tickets to the same screening separately, but still only received $2 credit.