I was browsing photos on Flickr and stumbled upon the $2 Portrait project. The idea was started by a photographer who decided that if anyone would ask him for money on the street, he would give him two dollars and in return the person would have to pose for a photo. The project is also meant to increase human contact and interaction. The photographer not only takes the photo but learns a little bit about the subject and learn their story.
This is a cool idea, except that I would run out of money quickly. I would love it if somebody paid me to take their portrait.
I've often wanted to take photos of strangers on the street. This is certainly one way of doing it.