I'm an avid Advanced Aquarist reader...but I'm a really dorky person. Somehow I take pleasure in reading the differential equations behind aquarium stuff. They have some more down-to-earth stuff too. I just love how well-researched their articles are. Highly recommended!
www.advancedaquarist.comI occasionally peruse other aquarium sites, but usually get fed up with lack of scientific evidence for claims or with the same couple of people dominating all conversations (I really hope I don't do that).
I find ReefCentral to have its good qualities for certain topics.