I took the lid from a Charlotte Russe shoebox, flipped it down, and used it to hold. Presently I have one thing that is an actual holder, and then my other nail polishes to the side of that, with other things that get used on it to the side. The whole shoebox lid thing is really convenient, because it means I can transport it between my room and its home on my closet bookcase (I have a bookcase in there, yes, but it's used for various clothing items).
How do you keep your nail polish organized? I'm very curious about this!