Gmail by Google has an official and comprehensive list of Keyboard Shortcuts which makes it quite easier to navigate across Gmail and access the various functionalities. You can access all the Gmail and Google Reader Keyboard Shortcuts directly from within their web interface just by pressing the Shift + ? shortcut.
A page will pop-up as shown below. You need to Enable the Keyboard shortcuts to start using them right away inside Gmail, some might work with Google+ too. Keyboard shortcuts help you save time by allowing you to never take your hands off the keyboard to use the mouse. That’s a cool feature and many aren’t aware of this trick! 🙂
Click on the image to view in full size: (Check list on web)
Similarly, you can view the list of Official Keyboard Shortcuts for Google Reader. Just open Google Reader and hit Shift + ? to view them. (Check list on web)
Don’t forget to share this trick with your friends. 🙂