A number of states have media-shield laws that protect reporters (in some cases, and for some definitions of "reporter") from being compelled to testify about sources in state-court proceedings. I don't know as much about those as I'd like; a plus of looking at them is that there's some history illustrating how they actually work in practice. To take one facet of "who counts as media?" that varies between states, here's an investigation of which states' media-shield laws cover student newspapers and the like: http://www.splc.org/knowyourrights/legalresearch.asp?id=60

One issue that comes up for me is that the justifications seem a lot stronger in some cases than others. For example, leaking the Pentagon Papers has some kind of public-interest justification, while the reporter linked above who leaked confidential testimony from the Charles Manson grand jury seems more like he was just looking for something sensational that would sell newspapers. But if a kind of public-interest/whistleblower restriction were included in a shield law, that would add probably undesirable ambiguity.