Chrome: Prefer using a mouse instead of hot keys to navigate Chrome? Gmail Mouse Gestures is a simple but useful handy extension that adds three simple gestures so you can navigate your email with just your mouse.
Gmail Mouse Gestures replaces a Google Labs tweak that has since disappeared. With it, you can press the right mouse button, and then drag up to go to the inbox, left for new mail, and right for older mail. It's simple, but works well if you're not a fan of hotkeys.