343 Industries has announced all the pre-order bonuses for Halo 4. The thing is, you're going to have to wait for the retailers themselves to announce which ones they have in the coming days. These are the known retailers to have announced their pre-orders so far, as compiled on the 343 Industries forums:
Worth noting is that the armor associated with the skins are not what comes in the pre-order, you get the skin associated with the armor. The colors on the skin can be customized to your liking. To see what they all look like, check out the gallery below.