Your basic choices are: low voltage DC, low voltage AC, and line voltage (110 VAC).
Before making a decision, consider:
Here are some obvious trade-offs:
Low voltage DC is quite safe. Even if you come into contact with a "live" wire, your body resistance will be so high that it won't pass appreciable current.
A lot of electronic gadgets operate internally from a low DC voltage. You might realize economies of scale by having as centralized source of (say) 12VDC, and running that everywhere. This has the added benefit of allowing centralized backup battery power.
Since most automobile, RV, boat, and solar power electrical systems run on approximately 12 volts, products are available that run on this voltage.
The problem with low voltage DC is that not everybody agrees what the voltage should be. So you often still require local power supplies.
If you distribute low voltage AC instead, you can boost or drop the voltage locally with transformers.
This is the most dangerous form of power transmission.
Given the ready availability of 110 VAC in homes, offices, and clubs, you can get just about anything that feeds on line voltage, mass-produced, low cost. This includes remote-control systems like X-10.
For example, "I have spooky eyes that run on a 9-volt battery, how can I reduce battery usage by plugging the spooky eyes into the wall socket?" - A classic requirement for low voltage DC. And "I found some surplus solenoid valves that run off of 12VAC, how do I get that voltage?" - A call for low voltage AC.
In both cases, the simplest answer is a "wall wart".
"Wall wart" is electronic slang for a small transformer with a plug attached, that hangs off of your electrical outlet.
A "wall wart" in its natural habitat.
Wall warts are available in a range of AC and DC output voltages. They are also available for low and high power.
We have a page devoted to wall warts.