Kill 5 opponents in a row without dying.

Killing Frenzy!

Kill 10 opponents in a row without dying.

Running Riot!

Kill 15 opponents in a row without dying. 

Rampage!

Kill 20 opponents in a row without dying.

Untouchable!

Kill 25 opponents in a row without dying.

Invincible!

Kill 30 opponents in a row without dying.

Killjoy!

End an opponent's killing spree - any spree.

Shotgun Spree!

Kill 5 opponents in a row with a shotgun without dying.

Open Season! (Formerly named Cheneymania!)

Kill 10 opponents in a row with a shotgun without dying.

Sniper Kill!

Kill an opponent with a Sniper Rifle or Beam Rifle.

Sniper Spree!

Kill 5 opponents in a row with a sniper weapon without dying.

Sharpshooter!

Kill 10 opponents in a row with a sniper weapon without dying.

Double Kill!

Kill 2 opponents within 4 seconds of the previous kill.

Triple Kill!

Kill 3 opponents within 4 seconds of the previous kill.

Overkill!

Kill 4 opponents within 4 seconds of the previous kill.

Killtacular!

Kill 5 opponents within 4 seconds of the previous kill.

Killtrocity!

Kill 6 opponents within 4 seconds of the previous kill.

Killimanjaro!

Kill 7 opponents within 4 seconds of the previous kill.

Killtastrophe!

Kill 8 opponents within 4 seconds of the previous kill.

Killpocalypse!

Kill 9 opponents within 4 seconds of the previous kill.

Killionaire!

Kill 10 opponents within 4 seconds of the previous kill.

Laser Kill!

Kill an opponent with the Spartan Laser.

Grenade Stick!

Kill an opponent by sticking them with a plasma or brute grenade.

Beat Down!

Hit and kill an opponent with a melee attack.

Assassin!

Hit and kill an opponent with a melee attack from behind.

Hijacker!

Board a vehicle.

Skyjacker!

Board an aircraft by forcably removing the opponent in it.

Wheelman!

Be the driver of a vehicle when a passanger kills an opponent.

Splatter!

Hit and kill an opponent with a vehicle.

Splatter Spree!

Splatter 5 opponents in a row with a vehicle without dying.

Vehicular Manslaughter!

Splatter 10 opponents in a row with a vehicle without dying.

Death From the Grave

Kill an opponent after you have died.

Extermination!

Get an overkill on the opposing team that results in all of the team being dead.

Perfection!

Win a slayer game with a score of 15 or more kills without dying.

Hail to the King!

Kill five opponents in the hill without dying and the hill moving.

Killed VIP!

Kill an opponent's VIP in a VIP game.

Killed Flag Carrier!

Kill the opponent flag carrier in CTF.

Flag Kill!

Get a melee kill with the flag.

Flag Score!

Score the flag in CTF.

Killed Bomb Carrier!

Kill an opponent bomb carrier in Assault.

Bomb Planted!

Plant the bomb in Assualt.

Oddball Kill!

Get a melee kill while holding the oddball.

Unconfirmed, but detected in code for Halo 3 Beta.

Killed Juggernaut!
Kill the Juggernaut in a Juggernaut game.

Bulltrue!
Killed an opponent that was in the act of a sword lunge.

Incineration!
Kill an opponent with a flame-based weapon.

Last Man Standing!
Be the last human in an infection game.

Sword Spree!
Kill 5 opponents in a row with the sword without dying.

Slice 'n Dice!
Kill 10 opponents in a row with the sword without dying.

Juggernaut Spree!
Kill 5 opponents in a row as the Juggernaut without dying.

Unstoppable!
Kill 10 opponents in a row as the Juggernaut without dying.

Infection Spree!
Kill 5 humans in a row as the zombie without dying.

Mmmm Brains!
Kill 10 humans in a row as the zombie without dying.

Zombie Killing Spree!
Kill 5 zombies in a row as the human without dying.

Hell's Janitor!
Kill 10 zombies in a row as the human without dying.

Is Quisnam Protero Damno!
Kill 15 zombies in a row as the human without dying. 

Medal images and medal descriptions provided by Bungie.