I love the Library of Congress's American Memory site--but I've always found it hard to find Montana-specific resources on it. So I was pleased to see that TPS-Barat chose Montana for its recent "State Spotlight."
They include links to images, maps, an oral history (recorded in Idaho but which includes information about Montana--including the 1918 flu epidemic in Helena), Montana newspapers digitized as part of the Chronicling America project, and more. You can check out their links here.
If TPS-Barat sounds familiar, it might be because you've heard me talk about their the Barat Thinking Triangle--a tool to help students analyze historic photographs--as well as the useful chart they created explaining how reading photographs aligns to the Common Core.