Staying at a hotel can be one of the most expensive aspects of travelling, especially if you go at the wrong time. Hotel search site Trivago researched the price changes for 46 cities around the world to offer us these travel advice calendars -- so you'll know when you'll get the best hotel rates.
The handy graphical calendars cover cities in Africa, Asia, Europe, North America and South America. At a glance, you can see, for example, that hotel rates are lowest in the (northern) summer in Bangkok, and highest in Washington DC in May and October.
The site also offers a Hotel Price Index, which shows average overnight hotel rates for 25 cities in the US by month (currently, the index shows January through July, but you can see previous years of data to find a pattern).
You can save a good chunk of money by knowing when to go.