Level select:
Start a new game and enter !EVAH! as a case-sensitive name.
(including the exlamation points and capital letters)
 

Invincibility:
Start a new game and enter B4K42 as a case-sensitive name. 
The "God mode" selection will now be unlocked at the options sscreen. 

All bonuses:
Start a new game and enter 105770Y2 as a case-sensitive name. 
Note: The code contains the number "zero" and not a capital letter "o". 
All character biographies, vehicle specifications, FMV sequences, and 
concept artwork will be unlocked. 

Multiple codes:
Start a new game and enter more than one code together to activate each 
of them simultaneously. For example, enter B4K42105770Y2 as a 
case-sensitive name. 


Hovering:
Hovering (A by default) is VERY useful. It doesnt take any energy/ammo, doesnt 
overheat, it makes an exelent anti-infantry weapon. Probably the most incredable 
thing is that it enables the walker to 'hover' over water until you let go of (A). 
There are a few limitations that i have found, firstly, you cant drop from far up, 
and you cannot go far out(several feet into the t.v. feet)