Enter the following codes during gameplay:

SPAMFORREST - Instant Handbrake

BIG BOTTOM - Bodywork Trashed

GOOGLEPLEX - Under Water Ability

GIVEMELARD - Mega Bonus (loadsa Money)

SPAMSPAMSPAMSPAM - Pedestrians Glued to Ground

SMALLUDDERS - Giant pedestrians

SUPERHOOPS - Explosive pedestrians

IGLOOFUN - Hot rod (Huge Speed Increase)

FUNNYJAM - Turbo Pedestrians

IHAVESOMESPAM - Gravity has Gone Strange

MOOSEONTHELOOSE - Pinball Mode

CHICKENFODDER - Bouncy Bouncy

BUYOURNEXTGAME - Oh dear, Jelly Suspension

ILOVENOBBY - Pedestrians Shown on Map

RUSSFORMARIO - Pedestrian Electro-Bastard Ray

HAMSTERSEX - Blind Pedestrians

NAUGHTYTORTY - Pedestrian Respawn

INTHELOFT - Drugs

BOYSFROMTHEBUSH - Grip-o-matic Tires

TRAMSARESUPER - Pedestrian Harvest (Pedestrians Stick to Car)

ISLANDRULES - Vesuvian Corpses

RABBITDREAMER - Gravity from Jupiter

Type in 'JOYRIDER' at the network race-type selection screen and you'll get access to all cars for network play. You'll need to select 'all' cars in the options screen to use them. This works with manual or random car selection.