Heading to London for the Olympic Games this summer but can't find a hotel room? No problem. Renting a room, apartment, or entire house has never been easier, thanks to the abundance of vacation-rental sites.

One of the biggest players on the Continent is HomeAway; more than 50 percent of its 300,000-property inventory is in Europe—with a sizable selection both in the countryside and in urban areas. It's getting competition these days from Airbnb, which started in 2008 as something of a domestic couch-surfing site, but now lists increasingly polished residences across the globe. Today a full 75 percent of its bookings are international, with Paris, London, Milan, Barcelona, and Amsterdam being the most popular cities. What's more, you can now link up Airbnb with your Facebook profile to view properties listed by friends and friends of friends—taking some of the mystery (and anxiety) out of peer-to-peer rentals.

Meanwhile, websites such as and are banking on their local expertise and presence, offering good deals in up-and-coming neighborhoods throughout Europe, such as Berlin's Neukölln and London's Stockwell (where flats for two people were recently available to book for as little as $93 and $53 a night, respectively).

You may not even have to shell out a nightly rate at all. lets you exchange your own apartment or home for, say, someone else's villa in Tuscany, among other European locales. The basic service costs $159 per year for an unlimited number of property exchanges—no rental charges allowed. Says CEO and founder Debbie Wosskow: "We're swap purists."