Kayak has long offered a rate calendar for flights, so you can see how the price of your airline ticket will change if you travel on different dates. Now they're offering the same thing for hotels. Just search for hotels on the dates you're looking to travel. Each listing will have a little link that says "rate calendar." You can see it on this search I did for hotels in San Francisco in March. At the Westin, prices within one week ranged from $171 to $255.
Of course, if you must travel on certain dates, this isn't particularly useful. But if your dates are flexible this could be a good money-saving tool. Click here for more tips for saving money on business travel. And if you have ideas of your own, please add them in the comments section below.