First, enter the name GOURANGA to activate cheat mode. Now enter the following as your name before starting a level:

MUCHCASH Start with $500,000 (save, exit, then restart your game)
GODOFGTA All weapons, full ammo
GOREFEST More gore
EATSOUP Free shopping
BUCKFAST More aggressive peds
RSJABBER God mode
CUTIE1 99 lives
ARSESTAR Keep weapons after you die
FLAMEON Gives you a flamethrower
VOLTFEST Gives you electricity ray gun
IAMDAVEJ Gives you $9,999,999
TUMYFROG Gives you all of the bonus levels
SCHURULZ Double damage powerup
HUNSRUS Invisible
UKGAMER Gives you all 3 cities
BEMEALL Gives you all 3 cities
DANISGOD Gives you $200,000
MADEMAN Get all respect from 3 gangs
LASVEGAS Some people turn to "Elvis clan"
NEKKID All people naked
FISHFLAP Makes all cars small