I listen to -
This American Life
Wait Wait Don't Tell Me
Car Talk
Tell us more about your friends' podcast...
I'm a big fan of Stuff You Missed In History Class and Dan Carlin's two shows, Hardcore History and Common Sense (a libertarian-ish podcast about contemporary politics)
I loved History of Rome... it's now defunct, because the podcaster had a baby and, well... reached the end of the Roman Empire, but it's got hours and hours worth of back episodes to listen to.
Listen to Joe ROgan get stoned and talk your ear off about dumb shit.