Two-finger pinch to view and select Tabs.

In Safari 6, and Mountain Lion, you can use a two-finger pinch to view and switch tabs.

Once you pinch in Safari (assuming multiple tabs are opened) you will get a view similar to that of Safari on iOS, and you can navigate among tabs using two-finger swipes to the right and left, arrow keys or a mouse or trackpad. This is an interesting way to preview all open tabs without having to load them fully.

You can either press Return, click the mouse or tap to select the frontmost tab, or pinch out to stay where you are. You can also close any tabs by clicking the close button in their headers or pressing Command-W while in this view.