Although I haven't heard calls past a year ago, my favorites are:
3: "Wierd Allience" - Just plain strange. But hilarious. (November 8, 2005)
2: "Memorial Day / Swarm 2 / DaVinchi Cone" - "The traditional philly flop" makes me laugh whenever I think of it. (May 30, 2006)
1: "Crawlspaces and Cheesesteaks / Sopranos" - I think Crawlspaces & Cheesesteaks is one of the most funniest things I've heard on the radio in a LONG time. Follow it up with the talk about the Sopranos and you have an instant win. (March 28, 2006)
I realize the last two are very recent, but they're really great.