Sometimes it can be annoying having to enter Mission Control to cycle through the open windows of your current application. So try out this little keyboard shortcut.
Hold down the Command + ` keys ( ` is in between the shift and z keys on the current keyboards).
Don’t forget you can also use the Command + Tab keys to cycle through ALL open applications.
This feature has been tested using Mac OS X v10.7.4 which was the latest Mac OS release at the time of writing and also using the latest Internal and external Apple keyboards.