If you want but haven't yet downloaded the Halo 3 Legendary Map Pack and were already planning to get Ninja Gaiden II for Xbox 360 in June, Circuit City has a deal for you. When you pre-order Ninja Gaiden II, they'll e-mail you a code to get thenew Halo 3 map pack free (a $10 value). Of course, you could wait and see whether Bungie will release the pack for free in six months (as they have with all of their other maps) but this way you'll get it within a week...
