Actually, the comment about not having a guide for perpendicularity is not quite true for the Rockler jig I bought. You can see it at the link below.
http://www.rockler.com/product.cfm?p...6&site=ROCKLER
You don't just stick any old bit in a plexiglass hole. This jig comes with a bit that has a collar on it which serves two functions. It guides the bit perpendicular to the hole and it provides a stop so the bit won't go too deep. The bit they provide makes a clean hole with no splintering. I have made several shelf pin drill guides such as those that have been suggested and this Rockler jig works better and is easier to use than any of them. The only drawback I know of is that you have to accept the hole spacing and depth they provide. It isn't adjustable for different spacings.