Video embedding seems to be behaving weirdly on my system (possibly because of new internet security filtering they've installed at work), so I'm just going to link to two versions of Black Sabbath performing "Iron Man" at this year's download festival.
This one doesn't have video (just a still photo), but the sound quality is remarkably good: http://www.youtube.com/watch?v=v-ivni4m-Gg
(And at 7:09, it segues into "Fairies Wear Boots", which is another fave of mine.)
This one has video, and listenable sound: http://youtu.be/1MdnL4l4BOs
I get chills hearing the crowd chant the opening guitar riff.
Ozzy's starting to look a bit like an old dude who's wandered on stage in his pajamas, but his voice is sounding pretty good. And Tony Iommi...this guy is in the middle of chemotherapy for lymphoma, and he still rocks harder than most of us ever will.