Since my fish room is in an unfinished section of my basement there weren't any outlets along the wall where most of my tanks will be going. In fact, the only available outlets in the room were on the same circuit as my washing machine, which pulls about 10 amps by itself. I estimated that the number of aquariums I plan to eventually run in this room would eat up 7 or 8 amps, potentially more if I include one or two high-light planted tanks.
I'm taking my time with each upgrade to the fish room to make sure that I build in the ability to expand by adding more tanks if I want to later. (See my fish room sink plumbing as an example) I thought about running an extension cord from a nearby circuit, but ultimately I decided to have a dedicated, 15 amp GFCI circuit installed by an electrician. Although I'm doing all of the plumbing and building the racks myself, I don't like to mess around with electricity, especially at the service panel.
I had the receptacles mounted a little over 6 feet up the wall so that they would be above the tops of the tanks. With a 15 amp circuit just for my aquariums I'll have plenty of power for the 10+ tanks I plan to eventually run. I'll also have power for additional devices like a sprinkler timer and dehumidifier. Once I start setting up racks this wall will be a lot more full, and I'll be able to mount power strips to each rack without running extension cords along the floor or around the room.