Shop TOMS. You can buy the same shoes you would get elsewhere, but your purchases here will go to help a less privileged child.
Donate old shoes. Just because they are no longer fashionable or comfortable for you doesn't mean that someone in need won't use them.
Start an old-shoe collection drive in your community. Get people to clean out their closets of shoes they don't need anymore, and find a worthy local group that needs old shoes, like a homeless shelter or an orphanage.