I recently went into my daughter's room and found a complete mess on the floor. When I told her that she had to clean it up, I told her that this would be a good opportunity to clean out some of the toys she no longer plays with. Since it is not likely that my sons would want to play with her "girl" toys, I gave her a suggestion.
I told her that she could gather all her un-used toys, sell them on the internet or at a consignment store, and then she could spend the money on some new purchases. Within a hour, she gave me a bag full of toys that she wanted to depart with.
If I am not able to sell them on craigslist, I will take her and her bag of toys to a local consignment store in hopes that they will buy them. This is a great learning opportunity for her and a way for her to make a little money.