15G - Go for the Gold
Win a gold metal on a challenge map

25G - Out of the Blue
Once you have control of both portals, only enter the orange portal

15G - Rat's Tale
Find all the Rat Man dens.

20G - Is Anyone There?
Complete the game without ever taking a bullet.

5G - Saw That One Coming
Cause a rocket sentry to destroy its own rocket when the rocket has been redirected back towards it.

10G - The Camera Adds 10 Pounds
Knock a turret over with a security camera.

20G - Like a Rat
Trap yourself in a test chamber so that GLaDOS has to help you continue.

5G - A Feeling Like Floating
Dissolve a turret.

15G - Tests Like Chicken
Find the chicken's test results.

10G - Cupcake
Beat 5 advanced chambers.

25G - Fruitcake
Beat 10 advanced chambers.

35G - Vanilla Crazy Cake
Beat all advanced chambers.

Games for Geeks:D