A SDR could be cool too, and basically let it connect live to ISS when the GPS confirms its above. CPU and memory might be an issue, but getting some 145Mhz / 437Mhz SDR and an external antenna jack on the board could be a cool way of letting the device listen in when the ISS is above.

Definitely alot of directions you could go with it, looking forward to seeing what people do with the code!