Call of Duty: Modern Warfare 3 is a Steamworks game, so no matter where you buy it, you’ll have to activate it on Steam.
The game has a release date of November 8, 2011 unless you were one of the lucky Kmart shoppers who got it early.
Amazon has MW3 priced $59.99, which is the regular price. However, it comes with a promotional credit for $10, good on any other game download at Amazon. Note that the credit does expire, but not until next year.
The other deal is at Direct2Drive / Direct2Drive UK (Maybe UK. Not 100% sure). It’s priced $59.95 but if you sign up for a 30 day free trial of IGN Prime, you’ll automatically get 15% off all purchases at D2D, which would make Modern Warfare 3 only $50.96. To get Prime, you first have to sign up for an IGN account and then sign up for Prime. (EDIT: Also it comes with a free copy of COD4). (EDIT2: Also make sure to go under account options and uncheck the autorenewal option).
I’ve been playing a ton of BF3 lately but I like to mix things up. Still waiting on the beta for CS:GO also.
One other thing to keep an eye out for. I was reading on the Green Man Gaming forums and they said that they are working on getting Activision games on their store. GMG + a voucher code would be awesome.
Final thing, pre-loading has started already. So once you pick up the game just take your CD key and activate it on Steam. Get that game downloaded so you don’t have to wait on Tuesday. BTW they said COD Elite is free now.