These are the medals awarded at the end of a multiplayer match, and can be collected and stored in your profile.

Assassin: Hit and kill an opponent with a melee attack from behind
Beat Down: Hit and kill an opponent with a melee attack
Bomb Planted: Plant the bomb in an Assault game type
Bulltrue: Kill an opponent who is in the act of a sword lunge
Death from the Grave: Kill an opponent after you have died
Double Kill: Kill 2 opponents within 4 seconds of each other
Extermination: Get an overkill on the opposing team, wiping out all of the members
Flag Kill: Get a melee kill with the flag in a CTF game type
Flag Score: Capture the opposing team's flag in a CTF game type
Grenade Stick: Kill an opponent by sticking him/her with a Plasma Grenade or a Spike Grenade
Hail to the King: Kill 5 consecutive opponents in a single life from inside the hill before it moves in a King of the Hill game type
Hell's Janitor: Kill 10 zombies in a row as a human without dying in an Infection game type
Highjacker: Board an enemy ground vehicle
Incineration: Kill an opponent by using the Flamethrower
Infection Spree: Kill 5 humans in a row as a zombie without dying in an Infection game type
Invincible: Kill 30 opponents in a row without dying
Juggernaut Spree: Kill 5 consecutive opponents in a single run as the Juggernaut in a Juggernaut game type
Killapocalypse: Kill 9 opponents within 4 seconds of each other
Killed Bomb Carrier: Kill the opposing bomb carrier in a Assault Gamtype
Killed Flag Carrier: Kill the opposing flag carrier in a CTF game type
Killed Juggernaut: Kill the Juggernaut in a Juggernaut game type
Killed VIP: Kill the opposing VIP in a VIP game type
Killimanjaro: Kill 7 opponents within 4 seconds of each other
Killing Frenzy: Kill 10 opponents in a row without dying
Killing Spree: Kill 5 opponents in a row without dying
Killionaire: Kill 10 opponents within 4 seconds of each other
Killjoy: End an opponent's killing spree -- any spree
Killtacular: Kill 5 opponents within 4 seconds of each other
Killtastrophe: Kill 8 opponents within 4 seconds of each other
Killtrocity: Kill 6 opponents within 4 seconds of each other
Laser Kill: Kill an opponent by using the Spartan Laser
Last Man Standing: Be the last human of the game in an Infection game type
Linktacular (secret medal): Play in a matchmade game comprised of all Bungie.net users
Mmmm Brains: Kill 10 humans in a row as a zombie without dying in an Infection game type
Oddball Kill: Get a melee kill when holding the ball in an Oddball game type
Open Season: Gun down 10 opponents with a Shotgun in a row without dying
Overkill: Kill 4 opponents within 4 seconds of each other
Perfection: Win a slayer game with 15+ kills without dying
Rampage: Kill 20 opponents in a row without dying
Running Riot Kill 15 opponents in a row without dying
Sharpshooter: Snipe 10 opponents in a row without dying
Shotgun Spree: Gun down 5 opponents with a Shotgun in a row without dying
Skyjacker: Board an enemy aircraft
Slice 'N Dice: Cut down 10 opponents with the Plasma Sword in a row without dying
Sniper Kill: Kill an opponent by using a sniping weapon
Sniper Spree: Snipe 5 opponents in a row without dying
Splatter: Hit and kill an opponent with a vehicle
Splatter Spree: Splatter 5 opponents in a row without dying
Steaktacular (secret medal): Beat the opposing team by over 20 kills
Sword Spree: Cut down 5 opponents with the Plasma Sword in a row without dying
Triple Kill: Kill 3 opponents within 4 seconds of each other
Unstoppable: Kill 10 consecutive opponents in a single run as the Juggernaut in a Juggernaut game type
Untouchable: Kill 25 opponents in a row without dying
Vehicular Manslaughter: Splatter 10 opponents in a row without dying
Wheelman: Be the driver of a vehicle when a passenger kills an opponent
Zombie Killing Spree: Kill 5 zombies in a row as a human without dying in an Infection game type