This is a slightly odd site, to be sure, but the Age Gauge is also an interesting way to place yourself in the span of historic events. The premise is that you enter the day you were born, and the site calculates how old you were at certain moments in time.
Khan Academy, and its accompanying YouTube channel, contains more than 1,800 short videos on topics mathematical, biological, chemical, and even historical.
Companion websites accompany the material in a textbook. They vary in quality, but if you have a good one, your students can access some really useful supplemental material.
There’s a saying that if you want to understand the times, read the advertisements. Adflip is a site with an abundant number of advertisements from various decades, ranging from back to the 1940s all the way up to the present.