They say the best organizing system is one which you will actually use. I've tried two methods for storing circular needles. The first was a binder of plastic pockets each labeled by size. I didn't like that system because I have some older circulars which belonged to my mother and curling them into the pockets always puts kinks in the cords which would take a while to disappear when I used them. Circular needle are actually not my first choice, I prefer straight needles mainly because I feel they put less strain on my wrists. On the other hand, circulars often make more sense dependent on the project or for knitting in public. Poking strangers with your needles tips doesn't generally go over too well.
My second system was one of these:
It should have worked better, but keeping the organizer in my crowded closets wasn't as simple as I thought it would be. The needles often caught on other things when I took them out. The labels face the wrong way when you are replacing needles in the organizer. I tried an over the door hook in our spare room and realized I just didn't put them back when I was finished. I'm not sure why but for whatever reason it just didn't work for me.
I've now stumbled on a new system. In an attempt to stop my constant searching for needle gauges, I tied one to a ribbon, tied the other end to a large binder clip and clipped it to a book case in our spare room. The idea was this would be permanent so I could always find at least one of the many needle gauges I own. Later I started sticking needles inside the handle of the clip instead of in the hanging organizer. When I filled that clip I added a new one. So two weeks ago I went to an office supply store, bought a bag of the largest size binder clips, labelled them and I have six of them in place.
If I'm more consistent with this system I may add a few more clips to make the groups smaller. It's not pretty but if it works I don't care!