If I can tell a fish apart from the rest, I name it. Some of the fish names I'm most proud of are:
Orange GloFish: Torpedo
Bi-Color Blenny: Dantrell
4 Bangai Cardinals: Inky, Pinky, Blinky, and Sue
Firefish Goby: Flash (that fish can disappear into the rocks really quickly)
Green Clown Goby: Midgee
Cave Goby: Dusty
Damsels: Ruckus, Butch (Butch has turned out to be one of the most cowardly fish in the tank)
Yellow Tang: Filet
I have two tangs in QT right now, I have a policy that they don't get named until I'm sure they're going to live through acclimation, and I also like them to "earn" their names somewhat. If these two make it I have names lined up for them. For the one that ends up being the boss after they join Filet (which I think will be the Atlantic Blue Tang, if Filet ends up being in charge I'll have to rethink this), his name will be Russell, named after Russell Hantz from Survivor. The other one will be named Buzz.