4e Podcasts
I listen to several podcasts on the D20 radio network. The two main 4e casts over there are Radio Free Hommlett and the Power Source. Radio Free Hommlett is currently on hiatus, although listening to some of their old casts would still be useful. I am not sure about the Power Source as I haven't listened in a while.
I also listen to the Dungeon Master Guys Podcast, The Dungeon Master's Podcast, 4 Geeks 4E, Critical Hits podcast and of course the official D&D Podcast from wizards. The Newbie DM Minicast is also a great resource.
As for podcasts with actual play, I listen to the Shattered Seas podcast and the Thursday Knights podcast. Return to Northmoor is an older 4e podcast but it walks through the design and actual play of a mini campaign.
These are some of the main podcasts that I listen to that are D&D 4e related. All of these casts are available through itunes. Unfortunately I don't have links to the web pages for these casts right now but hopefully this will get you started.