Become Ralph
Go to PASSWORD and put in LVPVS7890

Become George
Enter SM14N1230 at the password screen. 

Become Myukus
Enter N0T3T3210 at the password screen. 

Become Lizzie
Enter S4VRS4560 at the password screen. 

Alien characters
Enter B1G4L3210 and SRY3D3210 to unlock two alien characters.

Game Shark Codes:

Infinite Health 01647cd6 
Infinite Special Bar 01647ed6