Book the Conrad on the Hilton site before tomorrow comes around. Unless you are broke. I think Accor had/have a 40% sale in asia at the moment, I saw the Novotel for 60 USD a night. The sofitel and M Gallery and Pullman hotels in bangkok are surprisigly good for Accor hotels.

Where did you want to stay? If you have not been to BK before, choose a hotel (very) near a skytrain station and save yourself a lot of traffic headaches.

Rather annoyingly lots of hotel booking sites exclude Thai hotels from discount codes, so your best looking for the best straight deal you can find for bangkok if you need a hotel soon.