I was looking for a hotel in the Pratunam area and came across the following site with a pretty comprehensive list of 600 hotels in the greater Bangkok area :
Bangkok Hotels by Name - Hotels in Bangkok by Alphabetical Order
Lots of photos , reviews and maps to give you a clear idea of what you're getting. No need to book via the site but might prove useful if you have family or friends arriving. Combine it with google maps street view and you can also check out the immediate area.
I also noticed that a lot of the hotels I use are not on this list ( The Rex for example ) so this list is by no means exhaustive.