Any of the old Audio Technica dynamics (ATH-3, ATH-4, ATH-5/Signet TK22, and ATH-6D) are all the most comfortable headphones I've ever worn. Featherlight, zero clamp force, softest pads ever, very breathable and open. All-day wearing from a supra-aural, and I really mean that. These are in fact more comfortable than the HD800, in my opinion.
Other than that, HD800, most AKGs, any modern high end Audio-Technica, etc are all super comfortable.