There are a lot of good/great DJ apps for iOS, but if you're ready to graduate to physical control over your mixes, the iRig Mix is a good place to start. This lightweight, portable box offers crossfader, cue, EQ, and volume controls, can be used with a single iOS device or in a more traditional two device setup, and also offers an extra guitar/mic input, standard RCA outputs for direct connection to PAs or powered speakers, and, of course, a headphone output for master or cue monitoring.
The ODDIO1 is a cord-free headphone set that ONLY works with the iPod Shuffle. It's meant to be the coolest, simplest, cord-free workout experience. I really want to see one for the touchscreen iPod Nano, with buttons on the headset. $35 gets you a pair on Kickstarter.