You can open the page you are currently viewing in a new tab or window without closing it, using this shortcut. Basically you are duplicating the tab.
Click the address bar, alternatively you can press Command+L to set the focus on the address bar and then press either:
Option+Return » duplicates the tab into a new tab, or
Shift+Return » duplicates the tab into a new window.
I tested this with Chrome version 9.0.597.94 beta.
[crarko adds: I tested this, and it works as described.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20110214102729988