Marine Biology
OceanLink gives you pictures and lesson plans all about ocean life, from wetlands to hydrothermal vents, with a great glossary of Marine Biology terms.
http://oceanlink.island.net/
'Exploring the ocean frontier', this site connects visitors to real scientific expeditions and explores concepts that will open your eyes to thediversity of life in the oceans.
http://www.at-sea.org/default.html
NOAA's site dedicated to the images of marine life; exhaustive and beautiful. http://www.photolib.noaa.gov/animals/index.html
NOAA's national marine mammal laboratory site, complete with current research findings and load of images of seals, dolphins and whales.
http://nmml.afsc.noaa.gov/
This exciting and student-friendly site is geared towards saving the seas. Students can design their own deep-sea creature.
http://www.savethehighseas.org/deeptrouble/index1.cfm
The Marine Conservation Biology Institute has articles and news stories pertaining to saving the oceans' ecosystems; great photo library too.
http://www.mcbi.org/
Marine Crustaceans of Southern Australia! They may look like your garden variety, but look more closely and you'll see some strange ones indeed.
http://www.mov.vic.gov.au/crust/page1a.html