Thanks for the input, everyone. To answer some questions:
lowell, all 4 replacement rotors were new parts.
632 Regal, my wheels are the stock 15 in bottlecaps.

gale, when you say it is almost certainly a rotor problem, are you talking specifically to uscharalph, or would you apply that to my situation as well? I'm hesitant to replace the rotors again, as you might imagine, since it really didn't make any difference at all the first time. If it really does sound like a rotor problem, I would be inclined to believe that the rotor mounting surface itself is bent (though it doesn't look it...)

In any case, I think my next step will be to replace the thrust arms. As Alexlind123 said, since they probably need replacing anyway I might as well do that first and see if it fixes the brake vibration.

Thanks again to everyone for the advice.

Kevin