Some tonic water is the only way I know of and it only glows in the blacklight. I've seen some sites that sell glow in the dark cups - maybe they have some glow shot glasses. I've added some new Halloween-themed cocktail recipes to my website and will update at least once a week until Halloween:
http://www.halloweenguide.net/recipes.htm

http://www.halloweenguide.net
info@halloweenguide.net