Economic Uses of Algae- From the Department of Botany at the Smithsonian Institution. Very extensive site, includes cookbooks for algae!
"Red Tides" and Harmful Algal Blooms- This site is supported by the NSF, Woods Hole Oceanographic Institution and NOAA, and definitely is the place to start to learn more about Harmful Algal Blooms.
Pfiesteria- Go right to the source for information on Pfiesteria piscicida at this site from North Carolina State University’s Aquatic Botany page. NCSU was the first laboratory to identify this microorganism.
Red Tides- Information on other species, which cause harmful algal blooms.
Seaweed Site- From the University of Ireland, this searchable site allows you to find a plethora of information on "seaweeds." For example, when typing in Macrocystis, you can even get information on the use of this alga in ice cream!
There Are Algae in Your House- A lesson plan from the Smithsonian Institute pointing out the common uses of algae and their extracts.