The first of these we've heard of comes from GameStop. The huge game-selling juggernaut revealed its own special offer this morning. If you pre-order Modern Warfare 3 at GameStop in person, you'll receive a double-sided poster. Amazing! The poster will feature the standard Modern Warfare 3 art on one side, and, reportedly, a mocked up Time Magazine cover on the back. GameStop hasn't revealed the back side of the post officially, but JoyStiq has a picture that looks pretty legit to me.
(Thanks to reader Jake for the tip.)