Do you mean top five scams or top five signs of a scam?, because the two have very different meanings... I will assume the latter, and give you my answer:
1 - Anything involving a wire transfer where you're not the one receiving the money
2 - Any "offer" (particularly unsolicited) that requires you to pay money to make money or save money, such as home employment scams, mortgage remodifications, debt settlement, etc.
3 - Anything that comes to you unsolicited via email (great "deals," employment, etc.)
4 - No contact information, or only an email address
5 - Intense pressure to "act now" (one-time offers, threats, etc.)
If you want more in-depth information, my hub http://hubpages.com/money/Simple-Signs-that-You-Mi... has 9 simple signs and common examples to give you a pretty good feel for 90%+ of the scams out there.
Hope this helps! :)