I've seen the International Space Station (ISS) passing in the night sky a number of times, a fast-moving and super-bright object. It's a really cool sight. Today's APOD is a still based on a video shot through a small telescope by German astronomer Dirk Ewers. It's worth downloading and viewing the 1 MB video from that page to get an idea of what you're really seeing when that bright light sails by. The video is amazingly sharp.
The Bad Astronomy Blog recently explained how you can find out when the ISS will be visible for your location.