Fluorescein is a commonly used fluorescent dye that is quite hard to come by in a concentrated form. Fortunately, it's used in relatively large quantities in highlighter markers and can be extracted by a fairly simple process. Fluorescein makes spectacular explosions of color as it dissolves into water and can be used for many different purposes that are addressed in the video below.
For more demonstrations of fluorescein, also check out the following videos.
(Subtitled in English)
(An excellent tutorial to make Fluorescein in the lab)
In addition to the above videos, here are several links describing the process by which Fluorescein is used to detect trace amounts of blood, in case you want to read more on how it compares to Luminol in the field of forensic serology.