Here's a new take on the old bed and breakfast: AirBnb.com is an virtual marketplace that allows everyone to rent out their extra space—Facebook meets eBay. Evolving from airbeds a couple of RISD grads rented out to help cover their own rent, AirBnb now claims more than 50,000 registered users. With simple social networking tools and an honest review system, the site makes sleeping at a stranger's house seem down right enticing. With everything from slick city lofts and beach houses to yes, the occasional air mattress available for nightly stays, AirBnb offers a chance to experience your destination like a local (and for far cheaper than a standard rental). And what's more, some hosts even offer to cook breakfast.