How can you be sure the charity you are donating to is a legitimate one?

You can check two websites: Charity Navigator and the Better Business Bureau.

Charity Navigator reports on the accountability and spending of such charities.

The BBB has a page that posts standard of charity accountability.

You can also check the charity's finances. If they're a real charity or a nonprofit, they won't mind sharing them.

Also, remember to always use your credit card -- that way you can always dispute the charges.