If you're looking to cut costs in Europe (and who isn't anymore?), you may have considered hostels. One resource, europeanhostels.com, has been around since 1999. The site has just been overhauled and now has 38 European city guides, editor's picks, hostel photos, user reviews, and travel forums.
One thing that's really cool is the site search: Sort results by popularity, price, or user rating. Plus, you can view all locations on a Google map (also sorted by price) to find the location that fits you best. Other sites, like hostelworld.com, have maps, too, but they aren't sorted by price (and they're not nearly as user-friendly).