I get about 10 of these nigerian scam emails per day. And, the following is a link to a highly amusing website where they play games with the scammers:

http://www.419eater.com/

They email the scammers, pretend to be going along with the scam, and then tell the scammer that in order to be sure they can trust him, they will need a photo of him doing some odd thing, so they know the photo was recently taken.

So they have the scammer send a photo of himself holding a fish, or holding a sign which says "I love little boys", or some such thing, and they post the pictures on their website.