I've seen a layout published by Boeing for the 777-300 with 550 seats (the maximum certificated capacity) at 30" pitch.
Corsair are currently scouting for second-hand B77Ws to replace their B744s.
They don't want to take much of a cut below the 580 seats they have on the big old quad, so I think we can all guess at their preferred layout.
Correction to self: currently 582 seats including a business cabin!
http://www.seatmaestro.com/airplanes...oeing-747.html
Edit2: current 777 record holder is ANA with 525 seats in the domestic configuration. 19.3 grams of CO2 per seat-km, they say, compared to 22 for their DHC-8-300!