Tammy 2 from Parks and Rec, Dr. Spaceman & Colleen Donaghy (Jack's mom) on 30 Rock, Barry Zuckercorn on Arrested Development, and pretty much any secondary character on It's Always Sunny on Philadelphia (favorites are Artemis and the McPoyles).

Edit: Also, anytime Jeffrey Combs showed up on DS9 it was a goddamn delight.