Jerking the Trigger posted a look at Unity Tactical's Atom Mounting System. This allows for the mounting of a Red Dot Optic on the slide of a Glock. What makes Unity Tactical's system unique is that you are not stuck with any one single optic. With the use of interchangeable mounts you can switch between optics (if you'd like) or even mount standard iron sights back on the pistol at any time.
For more information I suggest you check out Jerking the Trigger's Post and Unity Tactical's Website (hopefully live soon).