I stumbled onto this Y-Combinator-funded site the other day and it looks pretty awesome.  From their site:

Airbnb is an online marketplace allowing anyone from private residents to commercial properties to rent out their extra space. The reputation-based site allows for user reviews, verification, and secure online transactions. Listings include vacation rentals, private rooms, entire apartments, bed and breakfasts, boutique hotels, castles, treehouses, and many other traditional and non-traditional accommodations.

How it works:

The open platform allows users to post listings of their space. Prospective travelers can search by city or country, utilizing filters such as price and room type to find exactly what suits their needs. Travelers contact hosts directly through the web site, which includes user profiles and friend recommendations. Dates are confirmed through on-site messaging, and the traveler books directly online using their credit card or PayPal account. Hosts receive a reservation request which they can accept or decline. Both parties then receive an itinerary on accepted reservations, and are set to go.

It’s been positively reviewed by a shit ton of publications and I would guess it beats traditional couch surfing or hostels due to the different options of dwellings you have to choose from.  So… yeah, helpful travel tip of the day.