I Love Green Guide Letters - Steele Saunders (seen live)
TOFOP - Wil Anderson (seen live)
Geeks Interrupted - Andy, Phil and Daniel
While it is actually commercial, Absolute Radio, Frank, Emily and Alun.
12.7 million downloads of their podcast weekly, with ads and music stripped out!
Bit of a male bias though, with the exception of Emily Dean, above.
I have just discovered a very entertaining female comedian in the the US. I Seem Fun - Jen Kirkman (will see live next year).
Thank you for saving my sanity during our long overseas flights.