Bangkok is one of those cities where there are fantastic hotels all over, several on Condé Nast top100 list. This being the Starwood forum, let's stick to discussing Starwood properties.
There's 102 pages worth of discussion (1518 posts), and I would recommend everyone to read at least the last 5-10 pages to get a good summary.
SGS and PA upsell Golds (and probably all guests) before checking in - Grand Deluxe is well worth the 1000thb or so. For mesmerizing views, I think only St Regis (some rooms) and ROS offer something easy on the eye.