Smithsonian-Folkways recently posted 24 one-hour podcasts exploring the history and archives of Folkways Records, a good candidate for the most important record label of the 20th century. And if you're a fan of the New Lost City Ramblers ... there pretty much are no other candidates.
I haven't explored these yet, but I sure want to. If you do some listening, let me know what you think. Episodes 3 and 11 seem to have the most NLCR.