You’re probably already using www.hotelsearchengines.net to search for hotels. It takes results from all the major hotel search websites and shows you which one gives you the best price.
If you don’t want to see all the cities in the world, then there are sites specific to cities and countries. Take www.switzerland-hotels-comparison.com for example. This site has been around since 2003 but has just had a revamp. Check it out.