Advanced aquarist is very good. I like to hit up google scholar too and browse, you can find quite a bit of research on aquaculture, not exactly aquariums, but there is still a nice bit that can be learned.
I have thousands of sites on marine species in my bookmarks.:)
I find new ones everyday. I have been posting on aquarium forums since 1985 before the web.:) Forums are good at sharing information with others but the knowledge is out there on the web in the wet corners.