Type cheats on the screen that says 'PRESS A KEY'. It may work on main menu too.
		
CHEAT	                EFFECT	
givemethedb9	        Get an Aston Martin DB9	(only DEMO)
givemethechargersrt8	Get a Dodge Charger SRT8 (only DEMO)	
canyonalltheway	        Enable Canyon race (only DEMO)
inthezoneskin           
syntecskin
5grand5grand
shinycarsarethebestcars
cooperlogofreeforyou
chasingmobile
guesswhoisback
trashtalking
bigredfiredrive
friendlyheadlocksapplied
nosforeverever
slowitdownwhenyouwant
speed3foryou
lotsoffreelogos
lotsoffreevinyls
watchoutthebigtruckishere
pharrellvinylgogo