An interactive version of Olaus Magnus’ 1539 Carta Marina, a map of the sea filled with the usual ( and unusual) monsters and creatures. (Slate)
MarineTraffic is a live map recording ship traffic based on AIS data. The site mainly covers European and North American coasts and includes info on vessels and ports, plus a gallery with some cool ship photos. Similar: see ShipAIS for live vessel movements from around the UK.
They that go down to the sea in ships, a really hauntingly beautiful collection of images of seafarers from the past. Some of the images have handwritten notes on the back as well. It's good to get a glimpse of the people and decades lived in by most of our grandparents. Who knows where all those digital images we all take will end up one day.