Simpilot:
One more to add to the list.
Harry Higley (Higleys Products) makes a set of 3 small drill guides that have various sized holes for different drills. All three are hexogonal shaped, giving you flat sides to set against the surface to be drilled.

I've been using a set of these for many years. They don't wear out, and their great for small jobs. Check them out at a hobby shop sometime.
Silversurfer