I have 2 girls and started buying Gymboree and then selling their clothes on ebay when they outgrew them. That way they could get more expensive clothes, but I could get some money back after they were done wearing them to buy more for the next year. I also love Target too sometimes, because you don't have to worry about their clothes if they ruin them at school, but those really aren't resellable.
I enjoyed buying and reselling so much, I decided to open my own boutique at http://www.youngandstylish.com