Three Tiers of perks with a total of sixteen options are found in Modern Warfare 2. These are Passive rewards that help benefit the player and the play still that is needed to help dominate the game. Each Perk has a Pro option that can be unlocked after completing some challenges.
Perk Tier 1

Marathon
Unlimited sprint.
Pro: Climb obstacles faster.
Unlocked: Default

Slight of Hand
Faster reloading.
Pro: Faster Aiming.
Unlocked: Default

Scavenger
Resupply from dead enemies.
Pro: Extra Mags.
Unlocked: Level 13

Bling
2 primary weapons.
Pro: 2 secondary weapon attachments.
Unlocked: Level 21

One Man Army
Swap classes at any time.
Pro: Swap classes faster.
Unlocked: Level 45
Perk Tier 2

Stopping Power
Increased bullet damage.
Pro: Extra damage vs. enemy vehicles.
Unlocked: Default

Lightweight
Move faster.
Pro: Quick aim after sprinting.
Unlocked: Default

Hardline
Killstreaks require 1 less kill.
Pro: Deathstreaks require 1 less death.
Unlocked: Level 9

Cold-Blooded
Undetectable by UAV, air support, sentries, and thermal.
Pro: No red crosshair or name when targeted.
Unlocked: Level 25

Danger Close
Increased explosive weapon damage.
Pro: Extra air support damage.
Unlocked: Level 33
Perk Tier 3

Commando
Increased melee distance.
Pro: No falling damage.
Unlocked: Default

Steady Aim
Increased hip fire accuracy.
Pro: Longer hold breath duration.
Unlocked: Default

Scrambler
Jam enemy radar near you.
Pro: Delay enemy Claymore explosions.
Unlocked: Level 17

Ninja
Invisible to heartbeat sensors.
Pro: Your footsteps are silent.
Unlocked: Level 29

SitRep
Detect enemy explosives and tactical insertions.
Pro: Louder enemy footsteps.
Unlocked: Level 37

Last Stand
Pull out your pistol before dying.
Pro: Use equipment in last stand.
Unlocked: Level 41