It appears they will have three different versions of Halo 3 next week. There's the plain vanilla version, with no extras, at the "normal" $60 price point. For another ten bucks, you can get the limited edition, which includes a DVD with making of stuff. For an extra $70, that's $130 total, you can get the "legendary" edition. It has the game, the behind the scenes stuff, a bunch of Red vs. Blue episodes, all of the cut scenes from all three games (including commentary from the development team), a featurette about working at Bungie, and best of all (kidding), a giant shiny Master Chief head that holds it all. How fun is that?
The fan in me wants the big one because of the composited story elements brought into one place, but that sure is expensive. And I'm not sure where I'd put the big head either. 