Type these at the main menu:

WOOWOO - Havoc Sirens

SUPACAM - Enemy FallCam

BENIHILL - Benny Hill cars

PANTALON - All Secret missions (in Training menu)

DOOBIES - Infinite Shields *

MRTICKY - Infinite Weapons *

STATTOE - In-game info

* You can't progress past the current mission when this code is enabled.