My personal fav era so far is 2005-2007. Radio wars with various other jocks, fighting with Howie, the XM walk-over which featured one of my all-time fav O&A show moments 'Anthony Loves Shawnee Smith' and the ensuing two hours of non-stop ball busting by Bill Burr and fans, the sound effects that they don't seem to use anymore (car crash, "Oh good Lord!", "That's terrible, I'm sorry", etc etc), making fun of Steve's Prius with the Jetson flying car sound, Jim RAMOOONE-ing boring guests.
lol....yeah, I loved that Louis bit too...."Mari-wanna..."
Of course Louis CK's best O&A moment of all time will always be his explanation of where the dreaded N-WORD came from. I can listen to that audio literally all day long over and over again for hours and it NEVER ceases being funny.