Ocean Planet:  A Smithsonian Exhibit
http://seawifs.gsfc.nasa.gov/ocean_planet.html
This exhibit covers ecological topics of the day.

The Mariners' Museum
http://www.mariner.org/
The Mariners' Museum, one of the largest international maritime museums in the world, is dedicated to "preserving and interpreting the culture of the sea and its tributaries, its conquest by man, and its influence on civilization.  Permanent galleries and temporary exhibitions all you to explore a variety of maritime subjects. 

Sea World
http://www.seaworld.org
This tour is part of the Busch Gardens Animal Information Database.  View sharks from the mini-cam or follow a whale.  There is even a Sea World songbook.

Mary Rose
http://www.maryrose.org/
Take the museum tour of the Mary Rose, the only 16th century warship on display anywhere in the world. Built between 1509 and 1511, she sank accidentally during an engagement with the French fleet in 1545. Her rediscovery and raising were seminal events in the history of nautical archaeology.

E-Quarium:  Monterey Bay Aquarium On-Line
http://www.mbayaq.org/
Wade into the pools or dive deep in the canyons of Monterey Bay.

Tennessee Aquarium
http://www.tennis.org/
One of the world's largest fresh water aquariums this site takes you through two living forests and past 9,000 animals that swim, fly, or crawl.