Report dating scam
The USA.gov's Internet Fraud Information page is a jumping off point for the reporting of crimes including phishing attacks, Internet investment fraud, consumer complains regarding internet marketing, scam e-mails, and much more.The site will link you to the appropriate agency's who handles crime reporting for each specific type of crime.
If it doesn't fall under one of their categories, they might be able to direct you to an agency that does handle it.
The e Bay Security Center: General Marketplace Safety site can assist you with reporting auction related fraud / and scams to the proper authorities and also provides a way for law enforcement to find out if someone is trying to auction merchandise stolen from you if you have been the victim of a property theft.
Nigerian scam comes in many forms: 419 scam, when they offer to transfer millions of dollars into your bank account, or lottery scam, when they tell you that you've won something in some bogus lottery.
Usually they say to keep some money for your trouble.
Needless to say, those Money Orders or checks are no good, and not even worth the paper they're printed on.