A great tip for Adobe Lightroom 4 Users. . .

Adobe Lightroom 4 has introduced a really easy way to find the White Point and the Black Point of your image by just moving a few sliders.
To find the White Point, go to the Basic Panel in the Develop Module and move down to the Whites slider. Now hold down the Option Key on a Mac or the Alt Key on a PC and click the center triangle. Your screen will turn either all black or black with white areas. These white areas indicate that there is no information (blown out).  Move the triangle on the slider to the left or to the right. We are looking for the first white pixel on an otherwise black screen. If there are still too many white pixels after the slider is moved all the way to the left, move up to the Highlights slider and repeat the same steps.

Repeat the same steps with the Blacks slider. In this case the screen will turn either all white or white with black areas. Move the slider back and forth until you get meaningful blacks. This one is a little more to your own taste. I like really dark shadows in my images, no detail, but that's me. You may want detail in all your shadows. Adjust the slider to taste.
Give it a try.