Portal 2 Cheats

Iron Grip (Bronze): Never lose a cube in Chamber 6 of the Mass and Velocity co-op course
Lunacy (Gold): That just happened
Narbacular Drop (Silver): Place a portal under your co-op partner while they are gesturing
No Hard Feelings (Bronze): Save a turret from redemption
Obstacle Building (Bronze): Complete all test chambers in the Excursion Funnels co-op course
Overclocker (Silver): Complete Test Chamber 10 in 70 seconds
Party of Three (Bronze): Find the hidden companion cube in co-op test chamber
Pit Boss (Bronze): Show that pit who's boss
Portal 2 Platinum Trophy (Platinum): Collected all other Portal 2 trophies
Portal Conservation Society (Bronze): Complete Chamber 3 in the Hard-Light Surfaces co-op course using only 5 total portal placements
Portrait of a Lady (Bronze): Find a hidden portrait
Preservation of Mass (Bronze): Break the rules in Test Chamber 07
Professor Portal (Gold): After completing co-op, complete Calibration Course online with a friend who hasn’t played before
Pturretdactyl (Bronze): Use an Aerial Faith Plate to launch a turret
Rock Portal Scissors (Silver): Win 3 co-op games of rock-paper-scissors in a row
SaBOTour (Bronze): Make a break for it
Scanned Alone (Bronze): Stand in a defective turret detector
Schrodinger's Catch (Bronze): Catch a blue-painted box before it touches the ground
Ship Overboard (Bronze): Discover the missing experiment
Smash TV (Bronze): Break 11 test chamber monitors
Stalemate Associate (Bronze): Press the button!
Still Alive (Bronze): Complete Course 4 with neither you nor your co-op partner dying
Stranger Than Friction (Bronze): Master the Propulsion Gel
Tater Tote (Bronze): Carry science forward
Team Building (Bronze): Complete all test chambers in the Team Building co-op course
The Part Where He Kills You (Bronze): This is that part
Triple Crown (Bronze): Solve 3 co-op chambers in the Mass and Velocity course in under 60 seconds each
Tunnel of Funnel (Bronze): Master the Excursion Funnel
Undiscouraged (Bronze): Complete the first Thermal Discouragement Beam test
Vertically Unchallenged (Bronze): Master the Repulsion Gel
Wake Up Call (Bronze): Survive the manual override
White Out (Bronze): Complete the first Conversion Gel test
You Made Your Point (Bronze): Refuse to solve the first test in Chapter 8
You Monster (Bronze): Reunite with GLaDOS
You Saved Science (Gold): Complete all test chambers in all courses of co-op

Alternate Title Screen
Beat the game for an alternate opening screen.

Singing Turrets
In one of the test chambers, you will see a turret in a ventilation shaft at the very beginning. If you use the laser and reflector cube to destroy it and go through the new opening, you can find some turrets rehearsing a song.