Codes for Midnight Club 3:
In options menu, go to cheat codes.

getheadj - Yellow smile
allin - Unlock Special Zone
dfens - Unlock Special Agro
getheadm - Snowman head
getheadn - Skull head
getheadk - Pumpkin heads
getheadl - Bunny ears
ontheroad - Vechicles take no damage
roadtrip - Unlocks Atlanta & Detroit
crosscountry - Unlock all cities in arcade mode
fillmeup - Max Nitro

Unlock Stuff in Midnight Club 3:
In Cruise Mode, find Rockstar R symbol to unlock various stuff.

Flag Vinyls - Find 12 Rockstar logos in Cruise Mode
Rockstar License Plates - Find 24 Rockstar logos in Cruise Mode
Race Starters as Riders - Find 36 Rockstar logos in Cruise Mode

Career Mode Unlocks:
Car Rims Set 1 - Beat Carlos in 3 of 3 Races in San Diego
Car Rims Set 4 - Beat Lamont in 3 of 3 Races in Atlanta
Car Rims Set 5 - Beat Roy in 3 of 3 Races in Detriot
Car Rims Set 6 - Beat Caesar in 3 of 3 Races in Detriot
Car Rims Set 7 - Beat Caesar the second in 3 of 3 Races in Detriot
Chopper Rims - Beat Naomi in 3 of 3 Races in Atlanta
Sportbike Rims -Beat Vito in 3 of 3 Races in Atlanta

Unlockables in Midnight Club 3:
68 corvette - win all the muscle cars of america races

Cadillac Escalade ext - win the second san diego tournament

Cadillac Escalade ext dub edition + $10,000 - win hotlanta tournament in atlanta

Cadillac Sixteen Get 100% Completion Chrysler 300c dub edition - win balboa park tournament in san diego

El Diablo Rigid - beat vanessa three times in career mode

Four-Twelve - Complete all 16 Exotic Races

G55 Amg - win all the truck races

Hotmatch Cuevito Motorcycle - Win all of Phil's 4 races in career mode

Lambougini Mercialago - Complete U.S. Champs Series (After Beating Detroit)

Cadillac CIEN - Beat the second tournament in Detroit Ninja

ZX 12R - win all the sport bike races

Nissan Skyline - beat all 13 tuner race tournaments

Skully - beat all the races for the Choppers of America Bike club

Lexus 1300 - Finish all of Vanessa's 1st 4 Races In Carrer mode