*  99 Lives: R2, L2, R2, L2, Up, Up, Up, Up, Circle
    * Sparx Treasure-finding (without doing Sparx worlds): Right, Right, Left, Left, Right, Right, Left, Left, Circle, Circle, Circle
    * Extra Hit Point (without doing Sparx worlds): Circle, R1, Circle, L1, Circle, R2, Circle, L2, Circle
    * Change Spyro's Color: Up, Left, Down, Right, Up, Square, R1, R2, L1, L2, Up, Right, Down, Left, Up
      The next button you press determines the color:
          o Green Triangle
          o Blue X (This cheat will cause you to exit the level, or quit the game if you're not in a level.)
          o Red Circle
          o Purple Square
          o Yellow Up
          o Black Down
    * Flat Spyro: Left, Right, Left, Right, L1, R1, L1, R1, Square, Circle

    * Big Head Spyro: Up, R1, Up, R1, Up, R1, Circle, Circle, Circle, Circle
    * Play Credits: Left, Right, Left, Right, Left, Right, Square, Circle, Square, Circle, Square, Circle
    * ACT (Automated Challenge Tuning) -- Changes the game's difficulty, which tells yourself how good of a player you really are, Circle, Square, Right, Left, Right, Square, Circle, X (To set to the harder difficulty mode, instead of the easiest, press the Square instead of the X)
    * Skate on a squid instead of a skateboard: Up, Up, Left, Left, Right, Right, Down, Down, Square, Circle, Square.

WARP
**This works after defeating the Sorceress(1st round)**
One cheat code, discovered well after the game shipped. Insomniac thought they had removed the level warp code, but nope, it's still in there. According to Brian Hastings, you begin by pausing, then punching in up, down, up, down, left, right, left, right, square and two more buttons, based on what you want to do:

Sunrise Spring Home: X, Circle
Sunny Villa: X, X
Cloud Spires: X, Square
Molten Crater: X, Triangle
Seashell Shore: X, Right
Mushroom Speedway: X, Down
Sheila's Alp: X, Left
Buzz's Dungeon: X, Up
Crawdad Farm: X, R1
Midday Garden Home: Square, Circle
Icy Peak: Square, X
Enchanted Towers: Square, Square
Spooky Swamp: Square, Triangle
Bamboo Terrace: Square, Right
Country Speedway: Square, Down
Sgt. Byrd's Base: Square, Left
Spike's Arena: Square, Up
Spider Town: Square, R1
Evening Lake Home: Triangle, Circle
Frozen Altars: Triangle, X
Lost Fleet: Triangle, Square
Fireworks Factory: Triangle, Triangle
Charmed Ridge: Triangle, Right
Honey Speedway: Triangle, Down
Bentley's Outpost: Triangle, Left
Scorch's Pit: Triangle, Up
Starfish Reef: Triangle, R1
Midnight Mountain Home: Right, Circle
Crystal Islands: Right, X
Desert Ruins: Right, Square
Haunted Tomb: Right, Triangle
Dino Mines: Right, Right
Harbor Speedway: Right, Down
Agent 9's Lab: Right, Left
Sorceress's Lair: Right, Up
Bugbot Factory: Right, R1
And ... the long awaited super-secret code ...
SUPER BONUS WORLD: Down, Circle
And ... the movies (in roughly the order you would see them playing the game)
Startup Movie: Left, Circle
"An Evil Plot Unfolds...": Left, X
"A Powerful Villain Emerges...": Up, Down
"A Desperate Rescue Begins...": Up, Left
"No Hard Feelings": Up, Up
"The Second Warning": Left, Square
"Bianca Strikes Back": Left, Triangle
"Byrd: James Byrd": Up, R1
"Hunter's Tussle": Left, Right
"Spike Is Born": Left, Down
"A Duplicitous: Larcenous Ursine": Up, L1
"An Apology: And Lunch": Left, Left
"A Monster To End All Monsters": Left, Up
"The Dancing Bear": R1, Triangle
"The Escape!": Left, R1
"Deja Vu?": Left, L1
"A Familiar Face": Up, Circle
"Billy In The Wall": Up, X
"One Less Noble Warrior": Up, Triangle
"THE END": Up, Right
"I think that's it. 'Spike Is Born' is the 'hidden' movie that was intended to play at the introduction of the 2nd boss, but never made it into the game. The only way to see it is to use the cheat."

Gameshark codes

Allows Game to Play in a Mod-Chip System [Note]   
D007AF6C 023A
8007AF6E 1000
D007AEE4 000A
8007AEE6 1000
Infinite Lives    8006C784 0063
Infinite Health    800705A8 0003
Extra Gems    8006C71C 3A98
Have All Eggs    8006C660 0095
Have All Sunrise Springs Gems    80071A10 0190
Have All Sunny Villa Gems    80071A14 0190
Have All Cloud Spires Gems    80071A18 0190
Have All Seashell Shore Gems    80071A20 0190
Have All Mushroom Speedway Gems    80071A24 0190
Have All Shela's Alp Gems    80071A28 0190
Have All Midday Garden Home Gems    80071A34 0190
Have All Icy Peak Gems    80071A38 01F4
Have All Enchanted Towers Gems    80071A3C 01F4
Have All Spooky Swamp Gems    80071A40 01F4
Have All Bamboo Terrace Gems    80071A44 01F4
Have All Country Speedway Gems    80071A48 0190
Have All Sgt. Byrd's Base Gems    80071A4C 01F4
Have All Evening Lake Home Gems    80071A58 0190
Have All Frozen Alter Gems    80071A5C 0258
Have All Lost Fleet Gems    80071A60 0258
Have All Fireworks Factory Gems    80071A64 0258
Have All Charmed Ridge Gems    80071A68 0258
Have All Honey Speedway Gems    80071A6C 0190
Have All Bentley's Outpost Gems    80071A70 0258
Have All Midnight Mountain Home Gems    80071A7C 0190
Have All Crystal Island Gems    80071A80 02BC
Have All Desert Ruins Gems    80071A84 02BC
Have All Haunted Tomb Gems    80071A84 02BC
Have All Dino Mines Gems    80071A8C 02BC
Have All Harbor Speedway Gems    80071A90 0190
Have All Agent 9's Lab Gems    80071A94 02BC
Have All Crawdad Farm Gems    80011A30 00C8
Have All Spider Town Gems    80071A54 00C8
Have All Starfish Reef Gems    80071A78 00C8
Have All Bugbot Factory Gems    80071A9C 00C8
Have All SuperBonus Round Gems    80071AA0 1388
Infinite Missiles vs. Shark Sub    80162330 0063
Easy Win vs. Shark Sub    D0162340 0010
80162340 0001
Easy Win Mushroom Speedway: Time Attack   
D006FA58 0001
8006FA58 0008
D006FA58 0008
8006FA5C 0008
D006FA58 0008
8006FA60 0008
D006FA58 0008
8006FA64 0008

Easy Win Mushroom Speedway: Race   
D006FA78 0000
8006FA78 0003

Note: You must have a 2.41 or higher version of the Game Shark to use this code. If your version of the Game Shark meets that requirement, and the code still doesn't work, then add "C1000000 0000" to the code.

All from my website http://www.spyrothedragon.wikispaces.com/