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 by Daughtry -or- Canadian Idiot by Weird Al Yankovich

Eva: Everybody Down by Nonpoint

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

Justin: Sexy Back by Justin Timberlake

Katie and Sadie: True Friend by Hannah Montana

Tyler: Radio by Jim Johnston

Izzy: Psycho by Puddle of Mudd

Cody: Sombody for Me by Nikelback

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

Courtney: Circus by Britney Spears

Harold: Pork and Beans by Weezer

Trent: Everybody's Fool by Evanescence

Bridgette: Pocketfull of Sunshine by Natasha Bettingfield

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

DJ: Where is the Love by The Black Eyed Peas

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

LeShawna: Please Don't Stop the Music by Rihanna

Duncan: Animal I Have Become by Three Days Grace

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

Gwen: Sweet Sacrifice by Evanescence

Owen: Fat by Weird Al Yankovick

Alejandro: Perfection by Cage9

Sierra: Taking Over Me by Evanescence

Chris: Money by I Fight Dragons

Chef: Stoned by Puddle of Mudd

Blaineley: Piece of Me by Britney Spears

Mr. Coconut: Dr. Coconut from Phineas & Ferb

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