I'll second Geopolitical Economy Report. Also, Revolutionary Left Radio is fantastic. The host, Bre is intelligent and charismatic, but more than that he's incredible at finding great guests and doing great interviews. If the episode topic even remotely interests me, the episode itself is almost always 9/10. He is also a part of two other podcasts, Guerilla History and Red Menace, which are also both great.
Blowback has had 3 seasons, all are fantastic.
Actually Existing Socialism has some good episodes, though they haven't been around for too long.
This one isn't expressly political, but The Dollop is amazing. Both the hosts are somewhere on the left, though I'm not sure exactly where. It is easily the funniest podcast I've ever listened to.
That depends on what they are doing and how they are doing it. If their only goal is to somehow bring about communism by winning a vote in a capitalist democracy, they are obviously ridiculous. But while living under a bourgeois democracy, while the population at large still believes in that system, participation in it can be used as a tool to build class consciousness, to work toward the ultimate goal of revolution. This is essentially Lenin's position in “Left-Wing” Communism: an Infantile Disorder.