two new ones:
HITSphere, which is focused on healthcare IT
HealthVoices, which has an interesting "Open Medicine" vision about healthcare. See their healthcare blog list here.

two older ones:
Healthcareblogs stopped refreshing its feeds for a while, but now it is back on track.
MedLogs which categorizes the blogs nicely between physician, nurse, biz, etc.

so, which one is the best?

HealthVoices, MedLogs, and Healthcareblogs all segment the various healthcare blogs well. Nonetheless, I think that niche aggregators like HITsphere are going to pick up steam. Healthcare is simply much too broad to aggregate it all for anyone to make sense of it all. Besides, most people only care about one or two professionals/specialties. I can only read so many M.D. blogs before I feel a little out of place.

Then again, maybe all of these will be leapfrogged by more sophiscated RSS aggregation technology, like a TiVo for webfeeds?