The International Space Station circles the Earth about every 90 minutes, and in that time they move in and out of range of a number of terrestrial radio stations. If you're ever curious what's broadcasting in the part of the world the ISS is moving over, Radio ISS will play it for you.
The site itself is pretty simple. Once you visit, you'll be treated to a view of the ISS live camera at Ustream, while the site shows you the position of the space station on a map, and streams terrestrial radio stations from the vicinity at the bottom of the page. If there's more than one available, you can choose among them, and you can watch as the ISS moves around the planet and the radio stations change based on its position.
Of course, this isn't quite "what the ISS hears", since that's a bit more complicated, but it is a fun little experiment to see what they may be hearing if they were to tune in to terrestrial radio somehow. It's also worth noting that not every station in an area will stream -- for example, when I tuned in and the ISS was just west of Mexico (shown above) the closest station streaming on the internet was an AM station from Texas. Hit the link below to give it a try and see what you can hear.