PBS’s “Frontline” regularly turns out incisive and fascinating documentaries, each of which is accompanied by an impressively deep microsite. These are more than just brochureware; they feature extended interviews, articles, charts, essays and reference materials. You could spend hours in any one of them, whether you’re interested in Hollywood, the Clinton years or global warming. They’re well-designed and content-rich, and great examples of how old media can get the most out of new media.