There is a site (your tax dollars at work):

http://www.spaceflight.nasa.gov/realdata/index.html

You can check the sitings link and see when it is going overhead. The kids and I have see it dozens of times. Just after sunset is the best.

Also you can see the realtime tracker on where it is at any one time. We saw the station while walking our dog. Got home 20 mins later and looked to see where it was. It was over Africa already. My daughters thought that was way cool.

Chuck