one lfs i went into had what looked like a 700gal or something close to it, with a full grown spiny lobster, about 8 fully grown lookdowns, and two medium sized brown banded bamboo sharks.
A great store near me carried mostly fish but also had tanks with turtles and...(dramatic pause)...baby american aligators! You have to be 18 to buy them though and I don't have nearly a big enough tank either.
That LFS carried mostly rare, unusual, or monster fish.
Fish wise i've seen lungfish, octopus, some halfbeaks, black tip reef shark (wasn't for sale),bamboo catshark eggs, pistol shrimp (not sure if they're rare but I had never seen one before), and some others.
I saw a 14" true albino oscar once at my LFS but somone had allredy put a deposit down on it probably so they could go make room for it. The same store also had some REALLY beautiful Dats, that had perfict bars on them.