Should probably get away from the old "...of 2009" thing, but this bit from Adam and Joe's BBC 6 Music podcast (aka "Podmax") made me laugh harder than anything else last year.
A quick iTunes podscan reveals my ears bathed in over 20 hours of A&J last year, with an estimated 12 of those hours spent emitting bizarre giggling sounds. Oh, go on, then:
Best podcasts of 2009:
1. Adam and Joe BBC 6 Music podcast
2. Everything else