If you are interested in finding the best garage door art ideas, there is only one company I could find online that does that sort of thing. You might be able to find someone n your local area that will paint a design on your garage but that is something most people won't want to bother with. They would rather have something they can buy and install themselves like the cool three car garage art below:
The company that does these can be found here Style Your Garage.com
Unfortunately, this is a German company so most of the designs are for single door garages because that is what most homes have in Europe. But they ship world wide including the United States, and this is something you will get in the mail and be able to install yourself.
They say it takes around 1 hour to install and you will probably need a couple of people to do it. Obviously the art for the 2 and 3 car garages would take longer to install than the ones for the single garage. If you are looking for cool garage ideas, this is certainly something to consider!