Glitch:
at las vegas, when you come out of the pits look for the 2nd set of cones to the left, line your car up about one car length to the left of the cones and you will get flipped ,,try diff angles to find the best air! now when you are in the air hold down the square , the car will begin to rock and if you are high enough you will begin to gain altitude, i did this and was able to hover for 2 or 3 min! this works at other tracks too.

Arcade-style beat the heat mode:
At the main menu, press Up, Down, Left, Right, R1, Left, Right. Cars can now hit the wall in beat the heat mode.

Shoot paintballs:
At the "Race Day" screen in single race or head-to-head mode, press Up, Down, Left, Right, R1, Up(2). Use your horn (press Up) to shoot a paintball. Alternately, select practice mode and press Up, Down, Left, Right, R1, Down(2) to enable paintballs.

Remove replay text:
At the main menu, press Up, Down, Left, Right, R1, Down, Up. Start a replay, then press Circle.

Unknown:
At the main menu, press Up, Down, Left, Right, R1, Right, Left.

Hardcore realism mode:
Get a 100 point rating on a track to unlock the hardcore realism mode option for that track.

Race as Richard Petty:
Successfully complete all Heat challenges with a bronze or higher rating to unlock Richard Petty.