Get Homer Car
Finish all 10 missions in mission mode. Go to Homer's pic in the car select screen to get the car

More time
hit phone booths that have a pic of Mr. Burns to get 2 seconds

Skip Mission
Fail a mission 5 times to skip that mission (except for final mission)

More Money
At the options menu Hold L1 + R1 and press Square, Square, Square, Square. A sound will signal correct code entry

Get Night Time
At the options menu Hold L1 + R1 and press X, X, X, X. A sound will signal correct code entry

Get Overhead View
At the options menu Hold L1 + R1 and press Circle, Circle, Circle, Square. A sound will signal correct code entry