3rd*
And I don't believe there is a 3rd interrupt available on the 328. If you want more interrupts, you'll need to upgrade. I know for sure the 1280 (Arduino Mega) has like 5 or 6 interrupts?
What are you trying to do with the interrupts exactly? There may be a way to utilize just 1 interrupt to handle multiple buttons.
For example.. if that's what you're doing.. using multiple buttons, you can use an analog input pin, set resistors on each of the buttons, and use analog-read to get button pushes. This way, you only use 1 pin for like.. 3 buttons or how many ever you're using, and anytime one of those 3 buttons is pushed, it interrupts, but only using 1 arduino pin.
http://www.nuelectronics.com/estore/index.php?main_page=product_info&cPath=1&products_id=2
Here's an example of a shield using that, it only uses analog pin 0 to read all the buttons.