Y.C.
Think of things you enjoy doing and are good at, then consider ways to monetize those skills.
I know one SAH mom who loves to cook - she caters small parties and bakes gorgeous cakes. I know another mom who contracts with people to do their wedding or event flowers (she used to work at a florist). I know a third mom who sings at weddings, funerals, and other events. Me - I take on occasional graphic design and editing jobs, working near a large university. And of course, I know several moms who provide daycare for one or two kids during the week - it doesn't have to be a full-blown daycare operation. Lots of people don't want to send their kids to a daycare center or a big home daycare where there are a lot of kids. You can use Craigslist to get the word out.
Just think about doing a little more of what you love!