Use rubbing alcohol and laser printer images to transfer image to nails. Brilliant! This could be an all-occasion thing. Some themes: pop art, comic book characters... Details here: http://blog.modcloth.com/2012/07/18/nail-klub-get-geek-week-chic-with-diy-nail-transfers/
Toothpaste Stain Removal - Certain nail polishes can really stain your nails in a way that cannot be cleaned by acetone. An easy way to combat this is to massage whitening toothpaste onto your nails, scrub them and rinse off (repeat if necessary).