Algae Research, Royal Botanic Garden Edinburgh
ADIAC Diatom Image Database
Algaevision (UK Algal Image Database, Natural History Museum: images to accompany The Algal Flora of the British Isles: does not include diatoms)
British Phycological Society
Cyanosite (including image gallery)
Paul G. Davison, University of North Alabama
The Delwiche Lab, University of Maryland
Desmids.com (Michael Ells)
Protist Information Server
Phycological Society of America
Phytoplankton Key: An image-based key to algae, cyanobacteria and other aquatic objects (A.L.Baker)