I've done two tours now - the Historic Bangrak Food Tour and the Offbeat Floating Markets Food Tour which I both throughly enjoyed. Sightseeing combined with food - what more can you possibly want! With the sheer quantity of eating places that Bangkok has to offer we would have never discovered the places we were taken to! I was busy making notes so I can find those places again and impress friends and family :)
Both guides were very knowledgeable and spoke English very well.