Late add: the German-originated ad-free podcasts include several English-language channels as well, covering not only language-instruction but culture, news, technology, science, and other topics.

Other national English-language broadcasters (NPR, PBS, CBC, ABC (Australia), etc.) have podcast channels, but most have succumbed to advertising. That isn't to say they don't have good programming, but don't expect ad-free listening. For a number of cultural reasons, Germany seems to have incorporated the idea that advertising itself has deep costs and its avoidance strong benefits.