I am about to get heavily into Aquaponics and thought I would start with a simple unit just to test things out.
Aquaponics: is the symbiotic cultivation of plants and aquatic animals in a recirculating environment. Alternate definition: An integrated hydroponics (growing plants in water) and aquaculture (growing fish) system. http://en.wikipedia.org/wiki/Aquaponics
Aquaponic systems can be small like this one or large commercial setups. I have found http://www.aquaponicshq.com
and invaluable source of information.
This system is very simple. Basically I put a box on top of my fish tank and pushed the pump through it and added some holes rocks and plants.