Plastic

The Story of Stuff Project’s The Story of Plastic
Plastic Free July (efforts can be applied year-round!)
Algalita, founded by Captain Charles Moore
Pollution

Litterati: A Litter Free World. Read my full post on Litterati!
Ocean

Water

National Association of Clean Water Agencies
Zero Waste

Bea Johnson @ Zero Waste Home
Kathryn @ Going Zero Waste
Catalog Choice (to stop junk mail)
Endangered Species

Jeff Corwin has many shows, several books, and is featured in a lot of online content. Follow him on his facebook page to see his newest adventures and missions. I reviewed one of his books and you can read my review here.
Joel Sartore, National Geographic and creator of the Photo Ark. Read my article about Joel Sartore!
The National Wildlife Federation
The Whale Sanctuary Project is working to establish a model seaside sanctuary where captive cetaceans (whales and dolphins) can be rehabilitated and live in their natural habitat. Read my article about them too!
Toxic Ingredients

The Environmental Working Group
Asbestos causes cancer and is in many of our homes and in the products we buy. Asbestos.com by The Mesothelioma Center is a for-profit site that provides many free articles and guides related to asbestos.
Education

GreenEcoWarriors.org: Their mission is “Creating a Culture of Sustainable thinkers” through education aligned with national standards. I learned about this organization from reading Pesky Plastic: An Environmental Story by the founder and CEO of GreenEcoWarriors.
The Union of Concerned Scientists
Fracking

Josh Fox, filmmaker, Gaslands
Environmental Law

Erin Brockovich’s website
Environmental Integrity Project