What kind of tail lights can I attach to the rear of my rack? Every taillight I've owned has mounted to the seat post, but when I load my rear rack the seatpost light is no longer visible. Instead, I'd like to mount a light to the rear of my rack, which has a single centered screw hole for mounting a light. What kinds of lights can I mount with this kind of setup? Are there lights specifically designed to be mounted on the back of a rack with a single screw?

The best picture I can find is below:
I recently bought a new rack specifically because my old rack had no good spot to attach a light to. Well, that, and it has a broken weld causing it to rattle.  The rack I bought is this one. I got the Bontrager Flare 2, which easily attached to the rack with a single bolt. The light has 3 modes, which are steady, strobe, and random. Random works well if you're riding in a group as the light can be too bright otherwise with all the LEDs on at the same time.  Also, check out this Tail Light Review on an amazing site.  The chart shows which mounting options are included with the light.