I just revisited Today's Progress Was Yesterday's Form Field; I had totally forgotten about Lemon's "angry dumbass" voice at 54:17. It's absolutely brilliant and needs to appear more often.
I'm pretty sure that he also used it when reading some creationist thing, but I can't remember which episode that was in. If I Could Turn Back Time, I'd Still Chop You in Half, and it sounds better there, too.