The Virtual Smithsonian gives a pretty neat overview of highlights at the Smithsonian Museums.
There’s audio, text, videos, images, and more covering space, history, and ancient civilizations (plus much, much more).
There’s audio support for a lot of the text, so it’s accessible to English Language Learners.
I’ve placed it on my Geography and United States History page under Sites That Cover Many Periods. The link is titled “The Smithsonian Museum.” This is not new to my site, but it’s one that can easily get lost among the 7,000 other links.