If you're the victim of fraud, make sure you file a police report with your local department! They may not be able to do anything right away, but if they receive enough reports from victims in your area, action will be taken.
Other places to report the crime:
IC3.gov (US) - A joint effort of the FBI and NW3C that accepts and investigates cyber crimes.
FBI (US) - Tips & leads form to report suspected fraud and internet scams.
eConsumer.gov - Submit your complaints here if you have been defrauded no matter what country. This is a multi-country cooperation for fraud complaints.
Canadian Anti Fraud Center (CA) - Canada's fraud reporting website for fraud within Canada (if fraud was initiated in Canada or the victim is Canadian)
Action Fraud (UK) - National fraud and cyber crime reporting agency for crimes within or involving the UK.
EC3 Europol (Europe) - Cyber crimes investigation unit for European nations.
ACORN (Australia) - Australian cyber crime online reporting.
Alert Africa - African network that provides useful information on scams out of Africa as well as resources for who to report crimes to (banks, providers, etc).
If you have fallen victim to an employment scam involving receiving/mailing checks or merchandise, picking up/sending money or similar "tasks", make sure to print out all emails and report it right away, do NOT wait for the authorities to look for you. You NEED to protect yourself!
Report to the US Postal Inspector - You can also report to the US Postal Inspector if at any point in sending/receiving involved the United Postal Service. Sometimes, even if UPS or FedEx was used they may still investigate so always protect yourself by reporting it.
Other sites with useful information for researching and information for victims:
419.bittenus - A site that keeps scammer emails, stolen photos and more to help bring awareness to scams.
Get Safe Online - A very good informative site that provides information and advised on protecting yourself against scams and cybercrime.
Scam Awareness Alliance - A site with information on scams and how scams work.
Scam Survivors - Another site dedicated to providing information and resources for victims.
Scamwarners.com - A community dedicated to providing information to the public on scams and they also keep an active forum of scams to look out for (with scammer email/contact information).
Stop-Scammers - A site set up to help track and report romance scammers.