Disclaimer: I have way too much nail polish, but I refuse to get rid of any old colors (you can always add a little nail polish remover to thin them out and they're good as new!).
My latest craft was to create a new nail polish holder by sprucing up a shoe box. All it took was a few coats of paint, and some glitter (as usual!)... and ta-da! I'm very satisfied with the result and it was such a simple craft.