HostelBookers

It's a great site that is easy to navigate and offers affordable locations with great accommodations.

I used Hostelbookers for my trip to Spain and was very pleased with the prices and locations themselves. Very easy to use. The only issue I had was when trying to book on the site it would some times get hung up and continue to spin for certain locations therefore not allowing me to book for certain hostels and then having to go with my second choice.
I'm planning a trip to Italy for the fall and will use their website again for all of my sleeping accommodations. This site makes my travel planning much easier. Thanks!