High Dynamic Range photography provides a larger visual tonal range than seen in the typical photograph.  Dynamic range is the difference between the bright and dark areas of your image. 

You can create images with more detail in the highlights and shadows than you can with a normal photo.

Merge several images taken at different exposures into one photograph.  Using a tripod is essential to ensure that each image is identical.   I usually take five photographs although I have taken as many as seven and as few as three.

        

Finished HDR image

Click photograph to see enlargement

Some more details:

There are several programs available that do a good creating HDR images.  A popular example would be  Photomatix.  At this point in time I am sticking to using only Photoshop.  Photoshop combines the photographs into a single 32 bit HDR image. I convert this into a 16 bit image after which a dialog box opens up offering some options for fine tuning the image to the way you want it to look.  Done carefully this process can be used to create spectacular images with a wide dynamic range of tones.  For a more detailed description of HDR check out Wikipedia.

The photographs shown on the b/w hdr rainforest page were subsequently converted to black and white and then into quadrotone.  Quadratone, a Photoshop option, allows you to pick other colors than pure black and white (in this case four colors). Other variations of this process include duotone and tritone.