About a year or so ago, I purchased a packet of glow sheets from either an office supply or craft-type store, and was really disappointed in how dim and short-lived the glow was. If I remember correctly, Alien Skin is a thick sheet material that glows brightly, and for a long time. I think it is also very expensive, though.
As a compromise, you might want to consider getting some glow paint or glow powder and painting whatever shapes/pieces you want to use. The high quality stuff can be really bright, and is available in different colors for extra creativity.
Vcal is the CPF authority on glow stuff, so you might want to ask him. You could also do a search on this board for threads regarding glow powder, etc. for further information.