Start game as usual. Prior to entering each of the following cheatcodes, go to the main menu, go to the Statistics sub-menu, go back again (pressing DELETE), and finally enter your desired cheat: 

Car    Code  
350Z 350350z 
Tiburon 667tiburon  
Peugeot 77peugeot 
Eclipse 899eclipse  
Focus 119focus 
Impreza 371impreza  
Lancer 222lancer 
RX7 777rx7 
Miata 221miata 
Golf 334mygolf 
Sentra 922sentra 
Neon 893neon 
Skyline 111skyline  
S2000 2000s2000 
Civic 889civic 
Supra 228supra 
240SX 240240sx 
Integra 342integra  
Nismo  givemenismo  
Celica 239celica 
RSX 973rsx777 
Petey Pablo gimmeppablo  
Lost Prophets needmylostprophets  
Rob Zombie gotcharobzombie  
Mystikal havyamystikal  
Circuits gimmesomecircuits  
Drag circuits gimmesomedrag  
Sprint circuits gimmesomesprints  
Drift physics in all mods slidingwithstyle  
Level 1 performance upgrades allmylvloneparts  
Level 2 performance upgrades allmylvl2parts  
Level 2 visual upgrades; no vinyls seemylvl2parts  
All Drift tracks driftdriftbaby  

Hint: Easy drift points:
Simply stay behind a car and watch the points rack up. 
Information in this section was contributed by the one braid bandit. 
Hint: Easy style points:
After you unlock the oval drift track, go into "Quick Race" and choose that track. Then, race around it using the handbrake to powerslide into the corners. Depending on how good you are, you will unlock rewards every time you fill your meter, which does not take too long.

Hint: Shoot smoke from nitrous:
To make nitrous shoot out smoke, put your car in neutral, or at the beginning of the race press [Nitrous].