The International Space Station (just left of the windmill) following the Space Shuttle Discovery (left of the ISS) over the Rottingdean windmill, East Sussex, Southern England.
I was so lucky! I didn't realise that I had got this shot, since I was busy looking down setting up the camera rather than up at the sky! By the time I looked up and saw them with my own eyes, they had passed out of the field of view!
The Shuttle and Station were on a very similar orbit, having only separated 12 hours previously.
Oh, and I got the Moon & Jupiter in as well!
Setup: 4 seconds exposure at ISO 800 with a Canon 40D