We're quite fond of both the iPhone and iPad versions of Traktor DJ. Rather than mimic the turntable rigs of yore, they're DJ apps admirably designed with interfaces tailored to touchscreen interfaces. Today, the app's developer, Native Instruments, announced small piece of hardware designed to control the apps.
DJ-ing is hard. Apart from buying all that expensive gear, the steep learning curve will keep many a budding turntablist out of most clubs (thankfully). So while the MiniMash app is awesome for doing the work for you, keep it away from my bars.