I tend to obsess over fonts and the latest obsession is Lato.
It was created over three years ago by Łukasz Dziedzic but I only discovered it recently when searching for something to use with my Live Maine Power Outages visualization.
The Lato main site provides desktop fonts and web fonts, but it’s also available at Google Fonts which—despite caving into Google’s insidious tracking—will probably make them load faster and save some bandwidth on your site(s).
Now I just need to import Lato into R and remember that I can tweak the matplotlib font config to use it with iPython as well.