Curves are by far, the most powerful and versatile color and tone manipulator in Photoshop. Many photographers like Erik Almas & Brooke Shaden swear by it, and is a major part of their workflow. Curves can be very intimidating at first, but once you truly understand how to use them, they will substitute the sliders of Brightness/Contrast, Color Balance, Shadow/Highlights etc. that you are used to.
In the newer versions of Photoshop, especially CS5 and above, there are many ways to use Curves. Photoshop Principal Product Manager Bryan O'Neil Hughes shows the lesser known tricks and techniques of using curves in this episode of the Photoshop Playbook. Watch this video to see how Curves can be your friend.