My current workout playlist, called "Shake It & Jiggle It", because that's basically what I'm doin when I'm up in the gym workin on MY fitness... here are some of my faves:

Dj Kool - Let Me Clear My Throat
Missy Elliott - Gossip Folks, Lose Control
September - Satellites (kinda techno-y)
2 Unlimited - Jump for Joy
Gnarls Barkley - Go Go Gadget Gospel, Transformer (I totally agree with sweet_talker, the whole album kicks.)
Andre 3000 - Hey Ya
Kelly Clarkson - Walk Away
Gwen Stefani - Bubble Pop Electric
Fat Joe - Make it Rain
Ciara - That's Right
kittycat Dolls - Wait a Minute
Shawnna - R.P.M.
Diddy - Diddy Rock

My absolute favorite song to workout to is Kanye's Workout Plan. That's my jam and always gets me pumped!!

alright some that haven't been mentioned here yet that I dug out of my collection:
Ain't no other man, Christina Augilerra
Hit me with your best shot, pat benetar
dancing with myself, billy idol
bring the pain, missy elliott
i will survive, gloria gaynor
mr. big stuff, gloria gaynor
virtual reality, rusted root
what I got, sublime