As first discovered by Nitrobeard, the special edition will include Oblivion, its two expansions (Knights of the Nine and the excellent Shivering Isles), a collector's steelbook, a making-of documentary, and a full-color map of Cyrodiil and the Shivering Isles. As a sticker on the front of the box shows, buying the 5th Anniversary Edition will also entitle you to $10 off the purchase of Skyrim and a strategy guide.
I might buy it because I never bought the expansion packs, and Oblivion was my favorite game...