By Troy DreirPaceDJ is an iPhone and iPod Touch app that creates mixes at your ideal target pace, letting runners, walkers, and cyclists synchronize their exercise with the songs they love. The app gets information from the iPhone or iPod Touch music library to determine the tempo of each tune. The user then sets a target exercise pace, either in steps or in rotations per minute.The interface is intuitive, so it's a snap to prioritize songs in mixes according to user preference based on whether users like or dislike what they hear in the mix. The app selects songs based on an energy ranking, which de-prioritizes lower energy tunes unless a user "likes" them. The app also lets user include songs at half-tempo and double-tempo of their target exercise pace. If this sounds good to you, jump on it: The typically $4.99 app is on sale for $.99 until July 24, 2011.