Traditionally, keyboards come with function keys - F1 through F12.
These keys are all wrong. It's not clear what they do, in any given application or OS. They take up valuable space and in my experience merely add confusion - they're way too abstract.
I would advocate the following four keyboard buttons instead:
Putting them clearly on the keyboard would make web browsing a much better experience, by reducing unnecessary use of the mouse.
It would also increase consistency with smaller devices, such as the iPhone or Blackberry - even if you don't have a QWERTY keyboard, you still need to navigate around.
And other applications - such as email on Blackberry - could easily use them too, bringing a standard user interface framework to computers.