These simple punches are incredibly useful when laying out things, yet nobody outside of machinists seems to know about them (some woodworkers know about the special ones for dowel holes). You can get them from most industrial tool distributors (like MSC), but they are also one of the early tasks for apprentices to make on a metal lathe.
Essentially, they are just a set of rods, in standard drill diameters, with a center punch tip in one end. When trying to drill pilot holes for things (say a shelf bracket) clamp it in place, and use them to mark the bolt holes. You wind up with marks dead center in the pattern, no more ovaling out holes so you can get the bolts through.
Similarly, there exist punches for transferring threaded holes – screw them in, and tap the sheet you want to transfer to.07/1/11