You named two really good ones. The other film by Michael Moore was pretty good too...."Bowling for Columbine"
There's an awesome documentary on HDTV2 on bears...but somehow i think nature documentaries might be out of the question.
Yesterday I watched the 1988 classic "Beavers"...a documentary on how they build dams. It was awesome.
if you're looking for someone to model yourself on then mark thomas has the light hearted documentary with serious issues down pat