What are good, reliable sources of information about him? Have the Indian tribes published anything or put anything online about their claim to him (other than court docs)? I know there are several books on the subject, but just how accurate are these?
In other words, what is my “cannot do without” resource?
(Can you tell I’m caught up in the drama about the whole thing? 
)
The National Park Service site provides a good review of the story. As you read the page, note that most of the titles of studies, reports, and press releases, and government orders are actually hyperlinks to (often) primary source material.
Here is another site dedicated to Kennewick Man (although I do not know whether there are examples of bias or special agendas buried in the site).