It's always possible to find a room for the night when you're traveling, but if it's last-minute, it'll cost you. Luckily, there are two apps that help you dig up deals for the right price.
Hotel Tonight (for iPhone and Android) focuses its search on the swankier side of accommodations, finding you deals on unsold rooms in hip, stylish, or boutique hotels.
You may have heard of my second choice, too: Airbnb, a peer-to-peer service that facilitates an owner's short-term rental of a space to guests (that's you). Unfortunately, Airbnb has recently been at the center of a terrible vandalism incident in which criminals posing as legitimate guests took advantage of the service to prey on a host. Although the victim is still recovering from the theft, Airbnb eventually did the right thing in revamping its policies to better protect hosts; it's ultimately a safer service.
There's always some risk when you use any peer-to-peer service (the same goes for Craigslist and eBay, not only couch-surfing sites), and I wouldn't discount Airbnb. In fact, the service and mobile app fill an important void in the casual renter's marketplace. As with most transactions of this type, it helps to continue to be aware.
If that hasn't scared you off, give the service a chance the next time you're in a tight spot, or traveling while on a budget.