A combination of:

• Here,
• Fodors (although the views on certain hotels is even more entrenched than here),
• Word of Mouth/Reputation (e.g. read any book on Bangkok and you'll see mention of The Oriental),
• Trip Advisor - mainly for the photos, but I think you can put more or less weight on some of the reviews which can help form a picture a view
• I also like checking out a couple of the hotels when I'm staying elsewhere in the resort / city - you'll get a feel for the feel of the place and the sort of people it attracts.

An additional site that I've discovered that seems to contain useful information is http://www.professionaltravelguide.com/.

Weighing up these and perhaps other factors such as Location, what's in the vicinity etc and balancing it against price / value (Crime doesn't Pay) means we're usually happy with our choice.