If you love animals and need some extra income then consider pet sitting. So many people need to travel for one reason or another even in a poor economy. Often times they are unable or don't want to take their animals with them. And in today's world, many people don't have close family that they can rely on to do this sort of thing for them. Another option is to find people who work during the day and have animals (especially dogs) that need to be let out during while they are at work. Some people would even be interested in a doggy daycare type situation in which you stayed with their dog or they brought it to your house while they worked! Yes, I've seen people on craigslist looking for this even in my fairly small town.
Some things to consider before getting into this business
You may want to consider getting some insurance in case something happens to the animals you are caring for, the animal bites someone while in your care, accidental damage to your client's property or if a client is at your home and becomes injured.
How to find customers
You can find customers in this business by word of mouth, asking local vets if you can display business cards at their front desk, craigslist. Another great source for getting local customers is by signing up with an online service that already has lots of traffic. Many people today look for local services by searching online first. Pet-Sitters shows up high in google search engines so people are likely to click on it and find your service in their area. I highly recommend signing up with them in order to find more customers.