"Spartan in Training- 50 GS: On Legendary, fight 4 Brute Cheiftains...and Win"
"Get Some!- 25 GS: On Legendary, kill a Brute Cheiftain and his pack with only a shotgun"
"Mean, Green, Killing Machine- 15 GS: Destroy an enemy vehicle with the Fuel Rod Gun"
"Happy Go Lucky Grunts- 5 GS: Kill a pack of grunts with 1 stick grenade"
"Keep It Clean- 15 GS: On Normal difficulty or above, assassinate a Brute Cheiftain"
"Stay Calm- 15 GS: On Normal difficulty or above, Spartan Lazer a Ghost charging at you"
"Sweep the Streets- 15 GS: On Normal difficulty or above, kill an enemy group with just a SOCOM Pistol"
"Scream, Aim, and Fire- 25 GS: On Legendary 4 Player Live Co-Op, Kill 2 Hunters with only grenades"
"Hunter Hunters- 25 GS: On Legendary, Kill all the Hunters in the game"
"The Brutes Been Shot- 25 GS: On Normal difficulty or above, kill a Brute with a brute shot"
"Stop, Drop and Roll- 5 GS: On any difficulty, get your first kill of the game with a grenade"
"Go Green- 5 GS: kill an enemy using the environment" (e.g. explosive barrels)
"No Spartan Shield Here- 15 GS: On Firefight, destroy a wall and the enemy behind it"
"Flashback Johnson- 20 GS: On Firefight, Use the Spartan Lazer before dying"
That's all i got, hope some of them are used
[Edited on 06.20.2009 9:59 PM PDT]