Firefox for Android & Yandex.Mail on Yandex.Store. Here you go three examples.
Humble Bundle hosts mobile bundles frequently (Android only). Although they are not as successful or popular as HB's PC games bundles, they certainly bring decent level of exposure and revenue to game developers outside the play store bubble. They're only possible because of side-loading.
I don't know the actual numbers, but I suspect Amazon's non Play Store apps are doing pretty decently.
Amazon's app store maybe?
Out of the frying pan - into another frying pan!
Yah so you trade Google garden for amazon garden. Not sure what that helped.