If you are building an electric vehicle go buy this wire chart so you don't burn up your wiring. Use this for DC battery to battery or motor wiring or when sizing your charging cord.
Since cobb brought up the PHEV charging issue here are plugs to match your wire.
Use this as a guide to set up battery chargers, deicer heaters, over the top block/coolant heaters.
If you look at that chart and only recognize 3 of those plugs don't worry. Unless you have serious 220v machinery you will never use anything more than nema 1-10, 5-15 and 5-20 serrries. Here is a short list of your most common high power receptacles and where you might find them.
Also lets try a little standardization.
For 30amp 120 volt plugs I would have to say your most common receptacles are going to be your nema series TT-30 and L5-30. Those are common camper and RV power cables. I also have also seen these on medium sized 120v only generators.
Your most common 220v generator plugs are going to be L14-20 and L14-30, any relatively new 220v generator that is big enough is going to have one or both. My troybuilt 7kw genset has both.
Your most common welder generator plugs are going to be L14-30, 14-50 and of course 6-50.
Your most common house hold sources of 220v volt power are going to be different depending on what kind of home and when the home was built or last time it has had a major rewire. Updated homes, trailers or homes built after 1996 are required to have 4 prong appliance receptacles. For your clothes dryer you will have 14-30 and for the electric range you will find 14-50.
In older pre-1996 homes your clothes dryer will have my personal favorite the classic 10-30 receptacle and the electric stove will have a 10-50.
(I use the NEMA 10-30 series on my welder, plasma cutter and air compressors)
Then you have your wild cards. The NEMA 6-15 and 6-20. These are the 220v versions of your standard 120v outlet. These relics refuse to die. They exist to power very large window air conditioners, usually in mobile homes and find them selves being used on 220v air compressors.
NEMA 6-50 is pretty rare, unless you find your self at a welding or fabrication shop, then they are everywhere. Some people install them in their garages and barns to power welding machines and plasma cutters.
My vote is for the L14-30. Specifically a flanged L14-30P "power inlet flange" installed on the vehicle or a length of SO or SJ cable with a L14-30P on the end spliced into the vehicles electrical system.
Because 4 wire 220v plugs are becoming the norm. You can also hot stab a L14-30. Standard 10-xx and non locking 14-xx series it is recommended that you "remove power" before plugging or unplugging, the prongs are long and heads of the plugs are small and its very easy to get your fingers around the edge of the plug head and onto live conductors.
Plus L14-30 is found on modern generators.
If for some reason you really did not want to install a L14-30 receptacle in your garage and wanted to use your 4 prong clothes dryer receptacle that is an option.
When I said "flanged power inlet" this is what I am talking about. Here is a L5-30 flanged power inlet I put on my little 110v stick welder. This idea could be applied to a vehicle for any reason you could want external power. L14-30 versions of this are pretty common too.
L5-30 is a locking 120volt and 30 amp plug if you need more power, L14-30 a locking 220/120volt 30 amp plug is also easy to find on ebay.
For powering block heaters eventually I want to use a flanged male L14-30 on my suburban. For now I just use a 10-30 clothes dryer cord on my over the top block heater. I may install an L6-30 on a car for its heater/deicer.