It only took me six years of knitting (and struggling to find the right needles), to properly organize my needles. I really don’t know why it took so long.
I bought a binder. I wanted something simple. This one is made out of cardboard. I’m not sure it’s that durable, but it will mostly sit on a shelf, so it works. I brought some sleeve protectors home from work. (They’re mine, not work’s. I just store them there since it’s more convenient). I printed up US and metric needle sizes on sticker paper, cut them up and stuck the sizes to the sleeve protectors.
All my knitting needles not in use on projects are now neatly tucked away in one place. There’s such peacewith getting things organized, especially when the rest of life seems so chaotic.