My kids absolutely loved making this Christmas gift! It only takes a few hours and cost me under $5 to make 9 rings.
A variety of old nail polishes (including clear coat)
A bag of large-sized clear gems (I got mine at the local Dollar Tree)
Ring backs (I got mine at Pat Catan's)
A hot glue gun
My 3-year-old schooled me in this project. See that really cool-looking ring below? She made it. By herself. All you do is flip the gem over to the flat side and start layering on the nail polish. Start with the lighter colors and get creative. Then add the darker colors, but make sure that each layer dries completely before painting on the next color. Paint the whole area with your last color (so that it looks uniform), let dry, and then paint with a clear coat to "seal" it. If you want to add a clear nail polish containing glitter (see bottom right of above pic), do so on the bulbous side after the flat side is completely dry (and then cover with clear coat). When rings are dry, attach the ring backs with a hot glue gun and Voila! You have a bunch of cute, handmade gifts to give away to some very lucky ladies :)
(I got this great idea from this tutorial on YouTube.)