1) Login to your First Facebook Account as always.
2) Now Click the Wrench to bring Google Chrome options, and Click New incognito window (or Press Ctrl+Shift+N)
3) By clicking New incognito window it will bring you a new private window that stores all cookies apart (cookie don't collapse with the first account's cookie) You'll notice a secret agent in the top left corner of Google Chrome.
4) Go to Facebook.com in the new private window, and Login to your second account as always.
NB: This method works also for: Gmail, Hotmail, Yahoo Mail, Twitter and many other accounting websites.