I just look on google for mash-up mixes and DJ tunes. Theres alot on there. DJ Earworm is a good one, DJ Dan, DJ Maggie Mash, Best of Bootie, DJ Greg J...
I also have a Napster subscription and generally the new music on there is stuff I listen to. Mika, David Bowie/Queen, Chemical Romance, Muse (Muse RULE!), Kate Nash, Marina and the Diamonds, Glee, (and though its not on there) the new Scissor Sisters album are all strong contenders for me at the moment. But my MP3 play list for the gym changes on a monthly basis, I'm always looking for new music.