The Tascam iM2X stereo condenser mic for the iPhone is only $39.99 right now at B&H (reg. $79.98). The iM2X records in 16-bit / 44.1 kHz through the free Tascam linear PCM recorder app and supports the iPhone 4, 4S and iPads through the third-gen.
This price has probably dropped due to the new lightning connectors on current iOS devices, but it’s still a solid deal if you are using an iPhone 4S/4 or an prior-gen iPad. Check it out here at B&H Photo.