http://www.wetwebmedia.com/marine/index.hm definatly a good resourse like fleashy said, though hard to find the info sometimes.
http://www.chucksaddiction.com/hitchhikers.html is a good refference for live rock hitch hikers, IDing good from bad.
I use these for general fish care/description refference (the don't have them all but they have a good chunk of common fish).
http://animal-world.com/encyclo/marine/salt.htm
http://www.aquaticcommunity.com/
http://www.chucksaddiction.com/disease.html for disease identification/treatment.
http://reefkeeping.com/index.htm has some good articels though they can be hard to locate.
All I can think of off the top of my head.
http://www.chucksaddiction.com/hitchhikers.html is a good refference for live rock hitch hikers, IDing good from bad.
I use these for general fish care/description refference (the don't have them all but they have a good chunk of common fish).
http://animal-world.com/encyclo/marine/salt.htm
http://www.aquaticcommunity.com/
http://www.chucksaddiction.com/disease.html for disease identification/treatment.
http://reefkeeping.com/index.htm has some good articels though they can be hard to locate.
All I can think of off the top of my head.