USB Stereo Microphone for iPad? What are working stereo USB microphone options for the iPad? It needs to be usable as an audio input into recorder apps? Presumably plugged into the iPad through the USB camera connection adapter.
Blue Microphones' Yeti and Yeti Pro stereo USB microphones can be used in any recording app on the iPad via the Camera Connection Kit.

The manufacturer confirms that this is possible, and has detailed directions for setting it up (including a video) on this page.

Note that you will need a powered USB hub.