Hacking skullduggery around the Halo 3 beta has revealed some new tidbits of information, including some of the single-player missions that may make it into the final game.
More specifically, a list of Achievements has been uncovered. In among the Achievements are what appear to be level names. Included in the list are: Jungle, Base, Outskirts, Voi, FloodVoi, Wasteland, Citadel, High Charity and a level on Halo itself.
Also included in the list of Achievements are the tough to find skulls, which in Halo 2 altered a level's gameplay.
The list of Achievements is unlikely to be final, since one of those listed bears the title "placeholder" suggesting there's still work to be done.