You all probably know this site, but I'll post it anyway:
http://www.marinetraffic.com

It's shows the AIS transponders on ships, so you can see where ships are
sailing almost in real-time. Although not every ship is equipped with a
transponder, it's interesting to watch this site if you're planning a
phototrip.

The site also let's you create a fleet of ships which you want to monitor
on a regular basis. Although I haven't gotten to it, it did seem usefull in
creating a fleet of tall-ships..

Before I go on my evening walk I usually view this site, so I can decide to
take my camera, or leave it at home.

Regards,

Jeroen