By default, the function keys on my MacBook Pro control various hardware features and native operating system applications like the brightness of the LCD, Expose, or iTunes. I like these buttons and can use the fn button to take advantage of application Function keys when working with certain applications. Some service-type, background applications also have useful keyboard shortcuts. I tend to forget which keys are active at the moment and sometimes launch the wrong processes.

Is there an application or operating system, native way of identifying all of the currently available keyboard shortcuts?