Tony Hawk's Underground [Xbox]

Perfect Rail Balance
Go to the options menu and in the cheat codes area enter letitslide.

Unlock Cheats
Get 129 of 129 level objective goals to unlock the cheats menu:
Cool Specials - Get 129 of 129 Goals
Moon Gravity - Get 129 of 129 Goals
Perfect Manual - Get 129 of 129 Goals
Perfect Skitch - Get 129 of 129 Goals
Perfect Rail - Get 129 of 129 Goals
Always Special - Get 129 of 129 Goals
Flame Grinds - Get 129 of 129 Goals
Rollerskates - Get 129 of 129 Goals
Kid Mode - Get 129 of 129 Goals

Unlock Hidden Characters
Complete the game's story mode to unlock hidden skaters
Gene Simmons - Complete Beginner Story Mode
Iron Man - Complete Normal Story Mode
T.H.U.D. - Complete Sick Story Mode

Unlock Hidden Levels
Hotter than Hell - Complete Story Mode (on any difficulty level)