PCWorld Magazine (story here) has a list of the Top 5 Online Scams:

1. Auction Fraud
2. Phishing Scams
3. Nigerian 419 Letters
4. Postal Forwarding/Reshipping
5. "Congratulations, You’ve Won a . . . " [Xbox, iPod, etc.]

The number of criminal charges filed for fake Ebay auctions is growing at an alarming pace, and while it is hard to believe, otherwise intelligent people (including at least one law professor) fall for the Nigerian (or South African, even Iraqi) requests to help transfer large amounts of money for a percentage of the loot. (ph)