I have a very weird mix on my mp3 -- everything from ABBA to Eminem

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Some of my faves (and yes, I'm a total dweeb) LOL!
Spice Girls - Wannabe
John Fogerty - Centerfield - I can't help but smile every time I hear this
Ok Go - Here it goes again (LOVE their video on the treadmills too!)
Barenaked Ladies - I love anything they do, and some are very upbeat (One Week, It's All Been Done, Life in a Nutshell, etc etc)
B52's - their new album (Funplex) is good, plenty of classics too (Roam, Love Shack, Rock Lobster)
Liz Phair - Extraordinary
Vampire Weekend
Lily Allen
Adam Ant
any classic 80's new wave, especially Duran Duran, Tears for Fears (their 1st album), old U2 (Joshua Tree or earlier), Alphaville, Thomas Dolby
Pearl Jam - Jeremy
The Fratellis (I think someone else mentioned them already?)
Black Eyed Peas - almost anything
Christina Aguilera - Candyman, Lady Marmalade
Gwen Stefani
Justin Timberlake - Sexyback
Greg Kihn - Breakup Song
Rick Springfield
Lady Sovereign - Love me or Hate me
The Police
For Cooldown (good idea Nik)
Norah Jones
Indigo Girls
any slower BNL
She & Him
Juno soundtrack
Amy Winehouse
Colby Callait - she's AMAZING if you haven't heard her
Scrubs soundtrack, especially Colin Hay (or get his own CD - he's fabulous)
Paul McCartney - anything
Suzanne Vega