An ever-expanding view of NPR's coverage of the issue, the stories and related materials are all collected here. There will also be, of course, substantial coverage on Morning Edition and All Things Considered.
As NPR's Sonari Glinton reported on Morning Edition, people have been lining up since Friday to be inside the court during today's session. SCOTUSblog has some early Monday morning photos of the scene posted here.
Some other resources:
— SCOTUSblog's "health care resource page," which includes "briefs and documents, argument previews and other archived coverage."