I have found the following links very useful!
www.wetwebmedia.com - GREAT SITE!
Wetweb has information on just about every aquarium topic. You can search their site for the info you are looking for, if you cant find it email them and their volunteer staff will try to help you find the info you need.
If you are a freshwater stingray fan you need to go here! This is a very nice site from the Netherlands. It has lots of info on freshwater stingrays, and some really big custom tanks.