Once again though, the Red Bull BPM HD / DJ Player apps are my preferred solution when considering playing out anywhere with the iPad.
In case you're having difficulty understanding the app or how to use it, there are a number of helpful instructional videos here. Full detail on the Red Bull BPM suite of apps can be found here.
All of the Red Bull BPM paid apps have a free version with pre-loaded tracks for you to test and play with before taking the plunge with the paid version. Personally, I think this is a great idea and helps sort out any misconceptions about what the app does and who it's aimed at.
Stereo Headphone AND Stereo Master output
Both HD and Pro versions offer a WiFi output option (0ms latency!) which transmits either the headphone/cue/PFL output or Master output in stereo via WiFi to another iPhone/iPod Touch/iPad, which means the device running the main app utilises the headphone socket for the Master or headphone output in stereo (ie whichever isn't being transmitted by WiFi!). As far as I know, currently no other DJ app offers a stereo Cue/Headphone and stereo Master output (via any means) at 0ms latency. This requires the Red Bull Master Out app installed on the second device;
Red Bull BPM Master Out is currently priced at $9.99;
OK...so take a deep breath...here's the Red Bull BPM suite (basically it's 3 different options each with a free version);
Red Bull BPM HD v2.0 (iPad only) is currently $23.99 (I thought it used to be $30.99 - so maybe has had a price drop);
Red Bull BPM HD Lite v2.0 (iPad only) is the Free version of the above app;
Red Bull BPM Pro v2.0 (iPhone, iPod Touch and iPad) is currently $9.99;
Red Bull BPM Pro Lite v2.0 (iPhone, iPod Touch and iPad) is the Free version of the above app;
Red Bull BPM Compact v1.1 (iPhone, iPod Touch and iPad) is currently $3.99 [this version has a much reduced feature set compared to the above versions];
Red Bull BPM Compact Lite v1.1 (iPhone, iPod Touch and iPad) is the Free version of the above app;
For price comparison; DJ Player v3.0 (universal app) is currently $29.99 and the NetOut (DJ Player equivalent to the Red Bull BPM MasterOut app) is $9.99.