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iPad App: djay ($19.99 - iTunes Link)

This is an awesome app. The best part is that it fully integrates with you iTunes music library. 

“djay transforms your iPad into a full–fledged DJ system and seamlessly integrates with your iTunes music library, giving you direct access to all your favorite tracks and playlists. A hyper–realistic touchscreen interface and ultra low–latency converge to offer you a true professional mixing experience, all with your own music. You can perform live, record mixes on–the–go, or enable Automix mode and let djay mix your favorite playlist from your iPod library auto–magically!”

djay for iPad - The full-fledged iPad DJ app by algoriddim (via djaysoftware)