Cheat: Perfect Skitches:
Enter rearrider on the cheats menu.

Unlockable: T.H.U.D. Character:
Enter NOOO!! on the cheats menu.

Cheat: Unlock All Movies:
Enter digivid in the Cheats Menu.

Moon Gravity Code:
Select "Cheat Codes" at the options menu, then enter "getitup" as a code. You can also get this code if you complete all 129 goals.

Perfect Balance:
Enter "letitslide" on the cheats menu.

Perfect Manual:
Enter "keepitsteady" on the cheat menu.

T.H.U.G. Music Code:
Enter "holeshot" on the cheats menu.

Unlock Gene Simmons and Secret Level:
Complete the Story Mode on Normal difficulty to unlock Gene Simmons from KISS and the "Hotter Than Hell" level. (In this level, find and grab the floating KISS letters to unlock a new video. You don't have to collect them in order. Collect the letters again to watch the band perform "God of Thunder" on the virtual stage.)

Unlock Hangar Level:
Go to Moscow and find the brown building near the tanks. Go around until you see the side where it is connected to X-mas lights. Climb up and grind the ledge toward the big building opposite of the tanks and jump into a window. Inside is the item that unlocks the level.

Unlock Iron Man:
Beat the story mode to unlock Iron Man from Marvel comics.

Unlock Pedestrian Skaters:
Find every Gap in the game (including in the hidden levels).

Unlock School 2 and Venice:
In the New Jersey level, go to the train station. Where the rails are at, on the left ramp in the middle column there is an item high above the ramp. Take the rail down to the ramp to get more speed so you can reach the item. (Or, climb on top of the awning which looks like a little white ledge, and walk along it and around the corner.) Get the item to unlock the School 2 level.
In the Hawaii level, find the tiki statue. Jump into its mouth and ride down the tunnel to the end. Get the item to unlock the Venice level.

Unlock Secrets:
If you complete all 129 goals, you will unlock the following:
Cool Specials
Kid Mode
Roller Skates
Flame
Always Special
Perfect Skitch
Perfect Manual
Moon Gravity

Unlock T.H.U.D.:
Beat the story mode on sick difficulty to unlock T.H.U.D.
Submitted by - Superfly Pete Frye

In the Carnival Level of THPS4, there's a way to get into the House of Horrors. Go to the right side of the House of Horrors, into the small alley. Do a move that knocks you into the side. In a few seconds, you should be transported to a small version of the House of Horrors.

Hint: Secret Tape Locations:
New Jersey - Go to the left side of the bridge; you will see a sidewalk next to the river. Jump down onto it and walk under the bridge.

Manhattan - Go to the Metro Center (the building that is very shiny and made of glass) the tape should be on the sign that says "Welcome".

Tampa - Find the huge building made of windows with two ramps in front of it. Air off one of the ramps (as if you were going to gap between them) and head high between the middle of the ramps.

Hawaii - Climb on top of the Big Surf Hotel and find the side facing the pink hotel. Then go into the corner on the roof next to the quarter pipe and look for a wire. Grind down the wire to the tape.

Vancouver - Find the big bubble thing with flags around it above the hockey rink, then find the quarter pipe next to it. Go out into the street and spine transfer the quarter pipe for speed and then air up to get the tape.

Slam City Jam - Locate the scoreboard in the middle of the stage and the circular platform that goes around it. Grind on the platform and into the bottom of the scoreboard.

Hotter Than Hell - Get onto the inner of two platforms that are high up in the air and head around the platform until there is a part where it starts to rise. Go up that part of the platform and get air to get the tape.