The $100 Limited Edition was revealed
[...] fancy box, a "UNSC Infinity Briefing Packet" [...]
The LE includes the "War Games Map Pack," a voucher for "three future competitive multiplayer map packs, each including three locations, available for download post-launch on Xbox Live." It also includes early access to six multiplayer Specializations, which will only be released at launch in this package; they'll be "released over time" to the general audience.
Other digital bonuses include an exclusive armor and weapon skin, an in-game emblem, and an Avatar prop. The LE also includes an "extended 90-minute version" of the Halo 4: Forward Unto Dawn video series, extra featurettes, and making-of videos.
Visit the link for a picture of the box.