The U.S. Fish and Wildlife Service has regulatory authority of all inland freshwater fishes in the U.S. This page contains links to all species listed as Endangered or Threatened by the Endangered Species Act (ESA). It also contains a link to candidate species (species that warrant ESA listing but are precluded by higher priority listing activities) and species that are proposed for ESA protection but whose listing packages are being reviewed by independent scientists and the general public.
NOAA Fisheries (also known as the National Marine Fisheries Service, or NMFS) has regulatory authority over marine fishes and anadromous fishes (such as Pacific salmon). This page has links to marine and anadromous fishes that are listed or proposed as Threatened and Endangered under the U.S. Endangered Species Act (ESA), and those that are candidates (i.e., species of concern) for ESA listing.
FINS (Fish Information Network)
FINS is an archive of information about aquariums.
Fish Link Central is a site you don't want to miss. You'll find links to hundreds of aquatics and fish pages. You can spend days here and travel the world, and find such unique and interesting topics as NANFA member Chris Scharpf's diary of his Amazon River collecting trip.
Biofilter.com: Aquatic Information Center
Lots of good info on shipping fishes, fish rooms, fish diseases, treatments, live foods, etc.