The Mathematics stackexchange has a blog featuring short expository articles about interesting pieces of mathematics. The articles are user-written. Now, I think part of our mission as a community, especially if we want to grow, needs to be to promote interest in the history of math and science, especially among other SE users. I thought maybe we could write some interesting blog posts to draw attention, perhaps we could also ask permission to link to HSM at the end, which I'm sure wouldn't be a problem, there's no reason math.SE should have a problem with promoting a sister site.
The style of the math.SE blog tends towards quite novel topics, the kind of mathematics that I'd usually call "cute" - ie, immediately accessible, at least in terms of why it's interesting. For example, the "stable marriage problem", or tetration. Thus, historical articles should focus on topics interesting to people without a pre-existing interest in history. I've left a few of my own ideas in an answer below.
The same sort of thing could be done for the physics SE, of course. Does it have a similar blog? Can we propose starting one?