Beat the Speed King. He drives the 1200 HP Skyline. You will get 3 million dollars and the ability to buy his car. It's not easy.
Alternate loading sequence
Hold R1 while selecting a transmission type. Keep R1 held through out the loading screen to see a man hanging from the roof of your car in first person view.
Analyze option
Pause the game immediately when you start a drive in quest mode. Scroll all the way down the pause menu to access an "Analyze" option under "Retire". This allows you to see the turning rate, accelerator, and brake pressure. This only works at the very start of the drive and you cannot turn it off once enabled.
Note: This may be dependent on the car type or parts.
Blue mosquito decoration
Hold L2 + X + Circle when choosing your shift assist option. Keep the buttons held until the game has competed loading. A blue mosquito with yellow sunglasses will be hanging from the roof of your car in the first person view.
Car part preview
Select the exhaust or aero at the parts selection screen. Press Triangle as the view zooms in to keep the camera away from the car. Press Triangle again to resume the zoom.
Control replay view
Start a replay in the driver view position, then press L1 or R1 to pan the camera.
Delete scores
At time record screen, hold L1 + L2 + R1 + R2 and press Start.
Display replay meters
During a replay, press Select.
Dog decoration
Hold L1 + X + Circle when choosing your shift assist option. Keep the buttons held until the game has competed loading. A dog with horns will be hanging from the roof of your car in the first person view.
Fixed replay view
Hold Triangle when the replay is about to start.
Full pause screen
Pause the game and press Triangle + Square. Press Triangle + Square again to restore the pause screen.
Genki Gremlin decoration
Hold R2 + X + Circle when choosing your shift assist option. Keep the buttons held until the game has competed loading. The Genki Gremlin will be hanging from the roof of your car in the first person view.
Mirror Buddies
While you are at the screen where you pick your transmission hold either r1,r2,l1,l2 until the now loading screen comes up. While your driving there will be a little beanie buddy next to your rear view mirror.
New nickname
Select any team sticker for your car and the team will get a new nickname.
Pink creature decoration
Hold R1 + X + Circle when choosing your shift assist option. Keep the buttons held until the game has competed loading. A pink creature will be hanging from the roof of your car in the first person view.
Siren
Set the rear spoiler to type 5 for the R30 and R30M, then use the horn.
Skyline car
Defeat the Speed King to get $3 million and unlock the Skyline car for purchase
View free run positions
At the course selection screen in free run mode, press Square to see the other cars.
View one-on-one battle positions
During a one-on-one battle, press Square to see the positions of all other cars.
White Carismo car
Defeat the last Zodiac (White Carismo) to unlock his car and get about $4 million dollars. To get $5 million dollars when you defeat White Carismo, let him win the first time he challenges you. Then go up, challenge him, and win. At the ending you will see a message appear that saying "Challenge Ending = 5 Million Dollars".