T.I. "Motivation" & "Bring 'em out"
The Strokes "Heart in a cage"
Hermes House Band "Country Roads"
Lil Jon & The Eastside Boyz f/ Ice Cube "Real *igga Roll Call"
Black Crowes "Lit Up"

These help me get through 4+ mile runs.

It's hard to pick just five...I generally rotate my playlists.
Here are some of my favorites:

Blestination - Cruel Summer (the Bananarama Remix)
Daniel Beddingfield - Gotta Get Through This
Nina Skye - Move Your Body
Superchick - One Girl Revolution
Bosson - One In A Million (Remix)

for workout music I recommend european dance music....

it's ALWAYS the best motivational tool for me...

.....and you don't have to tell anyone at the office if u just listen to it on the mp3 player at the gym....

.... here's a compilation series on itunes that I recommend:

http://phobos.apple.com/WebObjects/M...Club+Hits+Vol+

Bush was one of my favorite high school bands, and they have a Remixed CD that has all the songs I loved then overlayed with techno beats. Awesome for running stairs!