Recently Algoriddim just came out with a version of djay for the Mac platform, which is very affordable and I believe is great for both beginner and advanced DJs alike. The interface of Algoriddim's djay for Mac on a MacBook Pro I’ve been using the iPad application for over a year now on the Subway, Airplanes and on Road Trips in the car and its great for testing out mixes and playing DJ sets on the go.
Algoriddim’s djay is a Virtual Turntable / Software DJ Application that originally debuted for the iPad and iPhone, making it possible to DJ anywhere.