Tool, just for sheer innovation, plus unique tone on Justin's part and Daney's ability to keep the power on even when navigating very tricky rhythms.
Butler and Ward from Sabbath. Listening to Master Of Reality now and Ward's got some chops on him, and Geezer knows how to play melodically, well, but their ability to co-operate is why I'm mentioning them. Lots of great metal drummers listed here (Gene from SYL for example), but we're talking about rhythm SECTIONS here.
I wouldn't really call Led Zeppelin "heavy metal", even though some reviewer did once. Great rhythm section, but not a heavy metal band IMO.
If Rage Against The Machine are considered "metal", then I'd include them. Brad is a consistently underrated drummer and Tim.... requires no justification from me. When Sean Malone is playing in Cynic (which is almost never), I'd say he and Sean Reinhart (sp?) are definitely worth a mention too.