The next time you're planning a trip, head to Orbitz's Labs section and take a look at the Hotel Rates Heatmap. It might save you some cash by helping you figure out when the rates of your destination city are likely to be at their lowest.
The map is colour-coded from green to red to show lowest to highest rates, respectively. It charts these prices across calendar in the the last two years. Hovering your cursor over any cell will show you the exact rate in US dollars for that day.
The data is collected from listings on Orbitz, so it won't account for all specials. However, it's a great visual way to help plan your itinerary, especially if you have some flexibility in terms of when you travel.
Hotel Rates Heatmap [Orbitz]