I was a bit annoyed that Cmd–Tab, in Mac OS, cycled between applications, not windows, on Macs, and I was looking for a way to do this with windows instead. For example, if I have 2 Finder windows and one Firefox window, a shortcut that would bring me from the first to the second Finder window instead of Firefox.
I think I found something like this in the Finder's application menu. Well, when I clicked it, at the first glance, I think it did more or less that. The shortcut mentioned was ⌘+`. I can find the ⌘ key all right, but what the heck is `? I'm pretty sure I've tried the whole keyboard.
EDIT: The Macs I have tried this with are running Snow Leopard in French (Canada), and their keyboard configuration is very much akin to the Canadian multilingual standard one that I use on my PC, except for the fact that "complicated" characters are performed with Alt+key instead of Ctrl+Alt+Key/AltCar+Key, as it is on Windows.
Best Answer
Check your keyboard layout in System Preferences » Language & Text » Input Sources, where you can also activate the Keyboard Viewer shown below.
With the Canadian French (CSA) layout, the back tick key is to the left of Return while you hold the Option key (not the "highlighted" one — it's a dead key —, the one to its lower right).
With the Canadian English layout, it's to the right of the left Shift key, without modifiers.
For other layouts, enable Keyboard Viewer in the Input Sources screen of System Preferences, then open it via the the Input Sources menu bar item on the right, and try a combination of Opt, Ctrl, and Shift to find the back tick key.
Note that in System Preferences » Keyboard » Keyboard Shortcuts, you can change the keyboard shortcut for the window switching command.