Environmental organizations active in issues related to dolphins include:

The Ocean Conservancy
http://www.oceanconservancy.org

Blue Voice
http://www.bluevoice.com

Natural Resources Defense Council
http://www.nrdc.org

Earth Island Institute
http://www.earthisland.org

Greenpeace
http://greenpeace.org/homepage/

Whale & Dolphin Conservation Society
http://www.wdcs.org

American Cetacean Society
http://www.acsonline.org

Look at both sides of the captivity issue:

free the dolphins
Dolphin Project
http://www.dolphinproject.org

keep them captive
Sea World
http://www.seaworld.org

Animal Protection Organizations working on behalf of dolphins:

One Voice
http://www.onevoice-ear.org/english/index.html

Marine Mammal Stranding Centers:

The largest marine mammal stranding center in the world is near San Francisco but not many dolphins strand there (mostly pinnipeds).
http://www.tmmc.org

This New Jersey stranding center gets more dolphins:
http://www.mmsc.org

Government Agencies:

NOAA, Office of Protected Resources
http://www.nmfs.noaa.gov/prot_res/overview/mm

NOAA, National Marine Fisheries
http://www.nmfs.noaa.gov

Research Organizations:

Marine Mammal Research:

The Society of Marine Mammalogy
http://www.marinemammalogy.org

University of California, Santa Cruz
http://ims.ucsc.edu/rflml.html

Sarasota Dolphin Research Program
http://www.sarasotadolphin.org/default.asp

The Dolphin Institute
http://www.dolphin-institute.org/index.htm

Oceanographic Research:

Woods Hole Oceanographic Institution
http://www.whoi.edu

Scripps Institute of Oceanography
http://sio.ucsd.edu/

Monterey Bay Aquarium Research Institute
http://www.mbari.org/

Legal Issues:

The Marine Mammal Protection Act
http://www4.law.cornell.edu/uscode/16/ch31.html

Journal of International Law &Policy
http://www.jiwlp.com/index

General Interest Dolphin Information:

Everything Dolphins
http://www.everythingdolphins.com

Miscellaneous:

Our Publisher:

Infinity Publishing
http://www.buybooksontheweb.com