http://www.youtube.com/watch?v=tjGD_nWKj1Q

deej (App Store link) is an iPad & iPhone DJ app designed for beginners:

Most common controls of a professional mixing table are available on your device’s touchscreen. Play with the pitch and volume of your songs and even scratch or repeat your preferred tracks. You can start training on your own, and soon you’ll be able to invite your friends and play music at your own parties.

Features:

• All-on-screen interface
• 2 simultaneous tracks
• Pitch (+/-20%)
• Volume
• Single CUE point
• 3 band equalizer
• Main crossfader
• Scratch/seek spinner.