Here's the updated version of what I think all of the TDI character's theme songs are. Some people have two, though, because I couldn't decide which one was better.
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Ezekiel: home da Daughtry -or- Canadian Idiot da Weird Al Yankovich

Eva: Everybody Down da Nonpoint

Noah: Vicarious da Tool (I think it could be about his slightly sadistic qualities)

Justin: Sexy Back da Justin Timberlake

Katie and Sadie: True Friend da Hannah Montana

Tyler: Radio da Jim Johnston

Izzy: Psycho da Puddle of Mudd

Cody: Sombody for Me da Nikelback

Beth: Hazard to Myself (Don't Let Me Get Me) da Pink

Courtney: Circus da Britney Spears

Harold: Pork and Beans da Weezer

Trent: Everybody's Fool da Evanescence

Bridgette: Pocketfull of Sunshine da Natasha Bettingfield

Lindsay: My Boobs Are Okay da Lene Alexandra (I was going to put "Barbie Girl" but everyone does that one)

DJ: Where is the Amore da The Black Eyed Peas

Geoff: Fight for Your Right to Party da The Beastie Boys

LeShawna: Please Don't Stop the Musica da Rihanna

Duncan: Animal I Have Become da Three Days Grace

Heather: Sexy, Naughty, Bitchy da Tata Young -or- Cruella DeVille da Selena Gomez

Gwen: Sweet Sacrifice da Evanescence

Owen: Fat da Weird Al Yankovick

Alejandro: Perfection da Cage9

Sierra: Taking Over Me da Evanescence

Chris: Money da I Fight Dragons

Chef: Stoned da Puddle of Mudd

Blaineley: Piece of Me da Britney Spears

Mr. Coconut: Dr. Coconut from Phineas & Ferb

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If te don't understand any of them, I'll explain. Just ask. :)