My first post on boards.ie!
I would recommend "The News Quiz" from BBC radio 4 available on iTunes. Its a panel show, very funny and is definitely worth a listen.
"Keith and the girl", seems to be very popular, cant say that its hugely appealing to me, but my friends love it, not for the easily offended.
And for any science fanatics "The Skeptics guide to the Universe" is a good listen, dealing with all things new in the world of science and skepticism.
Actually all these are available on iTunes and ZenCast.