I listen to the following podcasts:
The Skeptics' Guide to the UniverseSkeptoidThe Amateur Scientist PodcastAstronomy CastBuzz Out LoudDungeons & Dragons PodcastNonsense PodcastThe Skeptic ZoneQuackCastHunting Humbug 101Dr Karl (ABC Science) Most are about science and critical thinking, and a lot of them happen to be Australian for some reason.
I used to listen to the Geologic Podcast but I'm thoroughly sick of listening to George Hrab talk about himself for hours, although I do miss hearing about the religious moron of the week. I think the Amateur Scientist Podcast is my favourite right now, mostly because it's so tittilatingly irreverent and sarcastic. I always look forward to Skeptoid too, because it's short and sweet and so well produced. Also, the D&D Podcast stands out right now because of the
Penny Arcade/PVP series (with special guest Wil Wheaton). Just listening to them play D&D is actually incredibly fun.