A good physical condition; patience; respect; will/concern to help people; a pretty stable psychological condition and not be too quick to anger and discrimination. A good critical thinking and ability to think quick and empathize.
That's really all I, a common citizen, can ask from cops, I think, and these were the qualities of all the good friendly and helpful cops who I met and who I'll probably never forget.
edit: I just clicked on thread from the links on the bottom, and I did not realize it was Ask A Cop. I'm obviously not a cop, but maybe it's still relevant.