We've had great luck selling things we don't need on Craigslist. We've also bought many things on Craigslist. I don't think I would put a lot of effort into turning it into a business, but in my opinion it's a great way to get rid of stuff you no longer need. We've sold clothes, baby gear, furniture, computer equipment, camera lenses, electronics, household items like bedding and table linens, toys, etc.
We've bought furniture (almost all the furniture in our house!), a bike, kids clothes and toys, several Christmas trees, speakers, etc.
I don't think I would look at it as a business, but it is a great way to get cash for stuff you don't need. The "free" section is great for getting rid of things you can't really sell anymore (we've been amazed how many people will show up for an old dresser or a beat up yakima box!!).