For some reason, I was going through my daily responsibilities until 'Progger...can't spell? ' came to my mind. Good times, I tell you.
I loved that. And the whole follow-up sequence of "Mike Portnoy...Jewish?" that led to Borlag zeroing my post-count was epic.
On a personal note, the hefdaddy facts were pretty fun.
I LOVED those.
Some others I will add:
The Pirate Ship thread on DTF.com before the split was pretty amazing too.
TransImperial April Fools (as well as some of the other 4/1 pranks)
The MSPaint new DT release series of threads
The MSPaint/Photoshop DTF members
Lots of other great moments captured in the archives subforum as well.