The page describes and shows the three standard kinds. The little metal cased pocket LED flashlight style is my favorite (pictured second one down on the page)-- works well and is small and portable. The top style is popular too and works fine. The screw in light bulb is my least favorite, because it isn't portable (though if you're in the dorms and have UV rock posters then you'd want it). You can find all kinds on amazon and ebay, and they are cheap. As mentioned in the article, all three give off the same ultraviolet light so it's just a matter of what style you want.
http://www.cycleback.com/blacklight/four.html