Case Western is rolling. Their committee meets about once a month and makes some offers each time. (I found out only two days after I interviewed)
U-Mich is rolling, though I'm not sure how often their committee meets (I think it was maybe a few weeks before I heard). I think they offer only a few "early" spots each time and roll some individuals over instead of rejecting flat-out.
U-Wisc operates a lot like U-Mich.
UNC-Chapel Hill holds two interview weekends back-to-back and then makes all of their decisions at once
U-Pitt and U-Penn finish all of their interviews before making any offers
If at all possible, I HIGHLY recommend that you apply to at least one rolling school (as long as there is one that you are interested in). Case's quick decision saved me from the expense and time of half of my interviews (considering I was really interested in their program). Plus, I think that it makes it easier to go through your other interviews knowing that, if worst comes to worst, you have a spot somewhere...