30GS - Pardon Our Dust: Get a Killionaire (assuming the multikill medals remain the same) using only Frag grenades.
7GS - Se7en With Se7en: Get seven Needler kills with seven needles in each kill.
10GS - It must look pretty!: Have an item in your fileshare favorited by Bungie.
30GS - THIS IS SPARTAAAA!: Get a kill streak of exactly 300 in Firefight. (i.e. a streak of 301 or more would not award the achievement. This would award at the end of the game)
50GS - Who needs help?: Do not use the Superintendent at all in the Campaign on Legendary. (if it's at all possible, of course)
0GS - Vidmaster Annual 2009: Complete the final level on Legendary, with everyone finishing in Brute Choppers and all skulls turned on.
30GS - Shut Up and Die: Mute everyone in the game in a free-for-all Matchmaking playlist and win the game with both a Steaktacular and Perfection medal.
30GS - Stand Still so I Can Kill You: Without moving from the start of the game, get a Killing Spree. (looking is ok)
Wow, this is fun...