I run 20 miles or so per week, mostly on rural roads in the day, but sometimes late-night (1am) in town. I briefly gave this some thought but ultimately decided that there just weren't many practical uses for a firearm except in the rare instance that you might need to inject yourself into an existing situation as a third party. I'm one of those odd folks that even most mean dogs seem to tolerate, so that isn't a huge concern. Male runners aren't really targets for BGs. First off, they're probably fitter than the BG. And second, they carry so little on them that the loot would never warrant the risk. I don't even carry music because I like to be aware of traffic/surroundings. And I doubt anyone wants my $25 Timex that bad, lol.
If circumstances dictated that I carry while running, I'd probably look into something extremely light and compact in a belly band. I'd consider the light 9's from KelTec, along with the KelTec/Ruger 380s. Gotta be light weight, gotta have zero movement.