Have you ever stored more than one extension cord on a hook? If you try to grab just one, either you'll leave loops of the cord you want on the hook, or you'll grab loops from more than one cord. This solves that problem.
Step 1: Make the Hangers
It is simple. You should be able to figure it out by looking at the picture.
Grab some rope or cord. Pictured below is approximately 1/4 inch 'clothesline'. Like a lot of my instructables, I used what I already had. Cut the rope into approximately 2 foot long pieces. Melt the ends if you so desire. Now tie each piece of rope into a loop. Use whatever knot you like. I think I used a simple overhand knot. Hold both cut ends in one hand, make a loop, pull the ends through the loop and pull it tight.
Step 2: Use the Hangers
Again, you can probably figure this out from the picture.
Coil up your cord using your favorite method (hmm... maybe another instructable?). I like to plug the ends of a single cord together for some reason. Maybe my dad does it that way, maybe granddad?
Once you're all coiled up, pass the hanger through the coil. Then, pass one end of the hanger through the other end. Hang it up by the end you just passed through the other end.
Another reason this is nice is that you can hang a bunch of cords off of a single 16d nail.
You're done. Now when you need an extension cord, pull it off the nail, undo the hanger, plug stuff in and make noise!
This method also works well for ropes, hoses and other long skinny coiled things.
Update: I feel silly because it has taken me so long to realize this...
When I take down a cord to use, I have historically taken off the storage loop and set it somewhere. Inevitably when I am done and go to put the cord back, I can't find the storage loop. Recently I've stumbled upon a simple solution. After undoing the storage loop, I simply pass the wall end of the cord through the loop before plugging it in. The storage loop is then easily found somewhere on the cord!