TripAdvisor is probably the best place to go for reviews; it also allows you to access the rates for select dates as advertised on some of the booking sites like Agoda.
What rather perplexes me is that for a hotel of this one’s stature, I seem unable to locate a website for it. The link offered in this New York Times review is not valid as of the October 26 (2011) date of my edit to this post. And this does appear to be the same website provided in an official Tourism of Thailand (TAT) website showcasing the hotel, so the New York Times was not in error.
For any major business to not have a working website is practically unheard of nowadays — very bad business.
Chiang Mai Plaza Hotel in Thailand
Uploaded by juril001 on Nov 10, 2007
This was our hotel in Chiang Mai Thailand. This had to be the most beautiful lobby that I have ever seen. Great staff.