How much postage is needed to mail an oversize greeting card?

The current postcard postage as of the new increase in Jan '09 is:

First-Class Mail® Postcards ($0.27 each)

Maximum size: 6 inches long by 4-1/4 inches high

First-Class Mail® Large Postcards ($0.42 each)

More than: 6 inches long by 4-1/4 inches high