Uncharted 2: Among Thieves - Free money

Use tweaks on a new difficulty:
You can use tweaks you've unlocked on one difficulty when you replay on another one. Start a new game and play until you get a gun. Go to options and change to the difficulty you unlocked the tweaks on. Enable the tweaks then save and quit. Change the difficulty back to the new one then select Continue.

Unlock Crushing difficulty:
Beat the game on Hard to unlock Crushing difficulty.

Infinite money:
If you do something in the game that rewards a lot of money, save your game if it is not an auto-save area then quit to the main menu. The load your game and do it again to get the reward as many times as you like.

Multiplayer Unlockables:
Reach a certain level and you can buy different unlockables in the multiplayer store:

Boosters:
Bandoleer (Booster Slot 2) - Reach Level 4; Costs $2,000
Break Up (Booster Slot 1) - Reach Level 10; Costs $11,250
Come Get Some (Booster Slot 2) - Reach Level 58; Costs $2,000,000
Deposit (Booster Slot 2) - Reach Level 40; Costs $98,250
Down the Irons (Booster Slot 1) - Reach Level 14; Costs $18,750
Evasion (Booster Slot 1) - Reach Level 50; Costs $210,000
Explosive Expert (Booster Slot 2) - Reach Level 20; Costs $32,250
Fleet Foot (Booster Slot 2) - Reach Level 16; Costs $23,250
From the Hip (Booster Slot 1) - Reach Level 6; Costs $5,000
Glass Jaw (Booster Slot 1) - Reach Level 57; Costs $1,500,000
Half Loaded (Booster Slot 2) - Reach Level 54; Costs $400,000
Hell Blazer (Booster Slot 1) - Reach Level 18; Costs $27,750
Invalid (Booster Slot 1) - Reach Level 52; Costs $350,000
Juggler (Booster Slot 1) - Reach Level 38; Costs $94,500
Keep Firing (Booster Slot 2) - Reach Level 12; Costs $14,250
Launch Man (Booster Slot 2) - Reach Level 28; Costs $58,500
Monkey Man (Booster Slot 2) - Reach Level 32; Costs $72,000
Point and Shoot (Booster Slot 1) - Reach Level 2; Costs $2,000
Rapid Hands (Booster Slot 1) - Reach Level 42; Costs $111,000
Revenge (Booster Slot 2) - Reach Level 48; Costs $134,250
Rocket Man (Booster Slot 2) - Reach Level 44; Costs $120,000
Scavenger (Booster Slot 2) - Reach Level 8; Costs $8,250
Scoped In (Booster Slot 2) - Reach Level 36; Costs $87,000
Situational Awareness (Booster Slot 1) - Reach Level 46; Costs $129,000
Sure Foot (Booster Slot 2) - Reach Level 26; Costs $52,500
Sure Shot (Booster Slot 1) - Reach Level 30; Costs $64,500
Treasure Bearer (Booster Slot 2) - Reach Level 24; Costs $43,500
Turtle (Booster Slot 1) - Reach Level 22; Costs $40,500
Veiled (Booster Slot 1) - Reach Level 51; Costs $300,000
Walk Softly (Booster Slot 1) - Reach Level 34; Costs $79,500

Skins:
Cameraman Jeff - Reach Level 30; Costs $100,000
Doughnut Drake - Reach Level 60; Costs $2,000,000
Genghis Khan Villain Skin - Beat Crushing Difficulty. Cost: 1,500,000
Harry Flynn - Reach Level 20; Costs $50,000
Heist Drake - Reach Level 10; Costs $20,000
Heist Flynn - Reach Level 20; Costs $50,000
Karl Schafer - Reach Level 50; Costs $1,000,000
Lieutenant Draza - Reach Level 50; Costs $1,000,000
Marco Polo Hero Skin - Get the Platinum trophy. Cost: Free.
Skelzor Reach - Level 60; Costs $2,000,000
Winter Chloe - Reach Level 20; Costs $50,000
Winter Drake - Reach Level 40; Costs $250,000
Winter Elena - Reach Level 30; Costs $100,000
Winter Flynn - Reach Level 30; Costs $100,000
Zoran Lazarevic - Reach Level 40; Costs $250,000
Zorskel - Reach Level 10; Costs $20,000

Taunts:
Flex Taunt - Reach Level 20; Costs $50,000
Flurry Taunt - Reach Level 30; Costs $100,000
Kiss Taunt - Reach Level 10; Costs $10,000
Pump Taunt - Reach Level 53; Costs $500,000
Yes Taunt - Reach Level 40; Costs $250,000

Achievements:

Bronze:

First Treasure
Objective: Find one treasure

Apprentice Fortune Hunter
Objective: Find ten treasures

Novice Fortune Hunter
Objective: Find 20 treasures

Cadet Fortune Hunter
Objective: Find 30 treasures

Intermediate Fortune Hunter
Objective: Find 40 treasures

Practiced Fortune Hunter
Objective: Find 50 treasures

Proficient Fortune Hunter
Objective: Find 60 treasures

Professional Fortune Hunter
Objective: Find 70 treasures

Expert Fortune Hunter
Objective: Find 80 treasures

Crack Fortune Hunter
Objective: Find 90 treasures

Relic Finder
Objective: Find the Strange Relic

20 Headshots
Objective: Defeat 20 enemies with headshots

100 Headshots
Objective: Defeat 100 enemies with headshots

Headshot Expert
Objective: Defeat five enemies in a row with headshots

Run-and-Gunner
Objective: Defeat 20 enemies by shooting from the hip (without aiming with L1)

Hangman
Objective: Defeat 20 enemies with gunfire by aiming while hanging

50 Kills: 92FS - 9mm
Objective: Defeat 50 enemies with the 92FS - 9mm

50 Kills: Micro - 9mm
Objective: Defeat 50 enemies with the Micro - 9mm

30 Kills: Wes - 44
Objective: Defeat 30 enemies with the Wes - 44

30 Kills: Desert - 5
Objective: Defeat 30 enemies with the Desert - 5

20 Kills: Pistole
Objective: Defeat 20 enemies with the Pistole

70 Kills: FAL
Objective: Defeat 70 enemies with the FAL

70 Kills: M4
Objective: Defeat 70 enemies with the M4

50 Kills: Dragon Sniper
Objective: Defeat 50 enemies with the Dragon Sniper

30 Kills: Moss - 12
Objective: Defeat 30 enemies with the Moss - 12

70 Kills: SAS - 12
Objective: Defeat 70 enemies with the SAS - 12

50 Kills: M32 - Hammer
Objective: Defeat 50 enemies with the M32 - Hammer

30 Kills: RPG - 7
Objective: Defeat 30 enemies with the RPG - 7

200 Kills: GAU - 19
Objective: Defeat 200 enemies with the GAU - 19

30 Kills: Mk-NDI
Objective: Defeat 30 enemies with the Mk-NDI

Triple Dyno-Might
Objective: Defeat three enemies with one explosion

Grenade Hangman
Objective: Defeat ten enemies with grenades by aiming while hanging

Bare-knuckle Brawler
Objective: Defeat 20 enemies with hand-to-hand combat

Steel Fist Master
Objective: Defeat 20 enemies with a single punch, after softening them up with gunfire

Thrillseeker
Objective: Complete one Competitive Multiplayer game

Buddy System
Objective: Complete one Cooperative Multiplayer game

Silver:

Master Fortune Hunter
Objective: Find all 100 treasures

Survivor
Objective: Defeat 75 enemies in a row without dying

250 Headshots
Objective: Defeat 250 enemies with headshots

Bare-knuckle Slugger
Objective: Defeat 50 enemies with hand-to-hand combat

Bare-knuckle Expert
Objective: Defeat ten enemies in a row with hand-to-hand combat

Master Ninja
Objective: Defeat 50 enemies with stealth attacks

Steel Fist Expert
Objective: Defeat ten enemies in a row with a single punch, after softening them up with gunfire

Charted! - Easy
Objective: Finish the game in Easy Mode

Gold:

Charted! - Normal
Objective: Finish the game in Normal Mode

Charted! - Hard
Objective: Finish the game in Hard Mode

Charted! - Crushing
Objective: Finish the game in Crushing Mode

Platinum:

Platinum
Objective: Platinum