Buy one get one free
Brice points us to TOMS Shoes.
I like several things about this approach. The simplicity of the offer, first of all. If you buy a pair of these very inexpensive shoes, he gives a pair to a kid in the developing world for free. No fine print.
Second, Tom has turned the shoe into a souvenir. A post-modern shoe, a shoe for people who don't need shoes, but are happy to wear a statement. This isn't the first pair of shoes most Americans will buy, it might not even be the tenth. But it will be one that people talk about when they're wearing it.