ABC News' Rebecca Jarvis reports:
In Chicago, families are making a few hundred dollars a month by renting everything, from their unused bikes to their backyards.
Kelsey Risher said she paid her rent with the money she made from turning her home into a doggy hotel through DogVacay.
"Some months, it's well over my rent," she said.
Risher signed up online and was then vetted by the website. For this particular week, Risher was sharing her home with a chihuahua-terrier mix named Ginger who'd been dropped off by the owner. Each dog she cares for earns Risher about $35 a day.
"It's a really, really nice alternative to leaving your dog at a kennel," she said about the service. Plus, she said, her price was often cheaper.
Across town, Tim White said he rents out his old bike for $30 a weekend through SpinLister. White lists the bike online as well as a pickup time.
"This past summer, I paid for the bike itself," he said.
The Sakofs told ABC News they rented their family's Nissan Altima out through RelayRides and had been able to put the extra money into a college fund for their son.
With RelayRides, the car owner sets the price, pickup time and location, allowing the renter to get the car directly from the owner. The car is even covered with RelayRides' $1 million insurance policy.
Though the Sakofs make $36 a day, RelayRides said the average user makes $250 a month and top earners make about $1,000 a month.
And not far from Soldier Field, home to the NFL's Chicago Bears, Kevin Sogor rents out his driveway to football fans using ParkatmyHouse. He made $400 last football season.
Even real estate rental site Airbnb helps you rent out your backyard to campers.
Experts caution however that rental regulations differ from city to city so make sure to check local laws before posting to any sites.