Books
These are some of my personal favourite/recommended reads.
Ocean-related:
Sea Change: A Message of the Oceans by Silvia Earle
The Secret Life of Lobsters by Trevor Corson
Behind the Dolphin Smile by Ric O'Barry
Blue Mind by Wallace J, Nichols
Coral Reefs by Peter Sale
Nature/Conservation:
We are the Weather Makers by Tim Flannery
Silent Spring by Rachel Carson
Fire Country by Victor Steffensen
Others:
The Most Good You Can Do by Peter Singer
Most Good, Least Harm by Zoe Weil
Animal Liberation by Peter Singer