Looks like new achievements have been leaked. May be final, may not be. Info is sketchy at this point.
30 Achievements totaling 750gs points have been revealed.
QUOTE
Heretic Skull
25gs
Citadel Skull
25gs
Assembly Skull
25gs
Sandbox Skull
25gs
Orbital Skull
25gs
Longshore Skull
25gs
Tank Dropper
25gs
Zombie Repeller
25gs
Delicious Brains
25gs
Save This Film
25gs
Have Fun Respawning
25gs
Killtacular
25pt
Awww, Too Bad
25gs
... Get the Horns
25gs
Post Mortem
25gs
Ghost Patrol
25gs
Blades of Fury
25gs
Pull
25gs
Hammer Time
25gs
Look Both Ways
50gs
Road Rage
25gs
Flag Dropped
25gs
Defend This
50gs
Came... From... Behind...
50gs
Alas, Poor Yorick
25gs
Double Double
25g
Vidmaster Challenge: Brainpan
25gs
Vidmaster Challenge: 7 on 7
0gs
Vidmaster Challenge: Lightswitch
0gs
Vidmaster Challenge: Annual
0gs
QUOTE
Double Double
On a Legendary map, got two Double Kills during a ranked or social match.
Came... From... Behind
On a Legendary map, got three assassinations during a ranked or social match.
Look Both Ways
On a Legendary map, got a Splatter Spree during a ranked or social match
Vidmaster Challenge: 7 on 7
Entered into a ranked or social playlist with 7 EXP on the 7th of the month.
Vidmaster Challenge: Annual
After 9/25/08, completed Halo on 4-player Legendary LIVE co-op, with Iron, and everyone in Ghosts.