Check out this video - http://www.youtube.com/watch?v=Ik7N2JRxq98 - it contains all 11 executions and how you are able to do them as follows:

Rude Awakening - Lancer + B

Meatsnap - A, then X

Curbstomp - Any weapon + X

Triple Punch C-C-Combo - Any non-execution weapon (shotgun) + Y

Snixecution - Sniper Rifle + Y

Torque Nudge - Torque Bow + B

Pistolwhip Deluxe - Boltok Pistol + Y

Boomshield Headache - Boomshield + Y

Shotgun Golf - Shotgun + B

Torquapitation - Torque Bow + Y

Sniper Head Thunk - Sniper Rifle + B