I just use whatever super glue gel I could find, probably from Lowes. It helps if you apply the bead of glue, dip it in water, then take it out. It's supposed to let the outer layer of the glue oxidize or something.

I always read the frag|super glue|epoxy|super glue|rock method worked well, but I never understood why you would put epoxy in between the glue if the glue was the only adhesive contacting the rock/frag.