Forums and email lists
Backyard aquaponics forum
If you are interested in adding an aquaponics system, I'd recommend spending some time on this forum. The people on the list are extremely helpful and have a great sense of humor. Be prepared to disappear into the site for long periods of time. The site is based out of Australia but there are members from all over the world.
Yahoo barrelponics group
This is another great group to join. There is a great manual available on the group to build a simple aquaponics system and the group is quick to answer questions and provide simple solutions to building issues.
Websites with aquaponics content
Aquaponics in Europe
If you are in Europe, this is a great new site with detailed information on how a system was built. There are lots of diagrams to inspire your building process here.
Hydroponics and aquaponics directory
This site has a large directory of various resources related to aquaponics as well as other sustainable practices such as square foot gardening