The Nike + iPod Sport Kit is available for pre-order for $29 and works with iPod Nanos. The website says you have to own or purchase a pair of Nike+ shoes, and Nike's just don't fit my flat, wide feet. They're made for people with skinny feet and normal to high arches. But since the only distinguishing feature of the Nike+ shoes seems to be a pocket under the insole to hold the wireless sensor, it certainly seems possible to hack another pair of running shoes to hold the sensor. I'll need to study a pair of these Nike+ shoes to see what's so special about the sub-insole notch.