I absolutely love the Eyeko Cosmic polish, it does look just like outer space on your nails. It's black with a fine holographic glitter in it, which looks silver until light hits it, then it looks loads of different colours.
I glued some little star-shaped rhinestones on too (from eBay) to fancy it up a bit. I really want to have really intricate pretty nails with loads of gems and stuff on à la Selina, but I'd probably knock them all off within five minutes. We shall see.