All  commands  are done via the console. They must be enabled via
the console option on shortcut, or enabled through the in-game options
under  the  Advanced  section  of  Controls.  It  is  then accessed by
pressing ~.
(Note: Most of these require sv_cheats to be set to 1.)


Cheat code:                        Effect:
change_portalgun_linkage_id <0-3>  Allow separate sets of portals 
                                   to be created
ent_create_portal_weight_box       Spawn Weighted Storage Cube
fire_energy_ball                   Fire an energy ball
sv_portal_placement_never_bump 1   Portal placement cannot be bumped
sv_portal_placement_never_fail 1   Portals can be placed on almost 
                                   any surface
upgrade_portalgun                  Allow use of second portal placement


Overheating Xbox 360:
     Play  the  level where you face off with the laser guided robots.
Once  you  get  past the first few robots, you must start dropping the
boxes  on the robots heads so that they fall over. In the little place
that  you  find  the first two boxes, crouch and walk behind where the
boxes  were.  You  will  find a little room with odd music playing and
graffiti  on  the walls that says things such as "The cake is a liar".
There  also  seems to be an Xbox 360 with a pot inside of it. The Xbox
360 is overheating and boiling the water.

Box head pictures: 
     On  the level where you get the companion cube after you run past
the  energy  balls and are in the room with the three elevators, there
are  two doors leading to a catcher, and a platform that is pushed out
of the wall. Walk up to the platform that is pushed out. Crouch behind
it  and walk through the opening. On the left hand side are a group of
pictures of people with boxes for heads and hearts around them.

Alternate title screen:
     Successfully complete the game to see the cake title screen.