Polarizing Filters

SLR cameras and some of the higher-end point-and-shoot cameras have filters that screw onto the front of their lenses.  There are a wide variety of filters, and one of the most useful ones is the polarizing filter (such as those in this non-affiliate link).

Oftentimes, light will reflect off surfaces and create a glare.  This often happens with bodies of water, and even in the sky on a hazy day.  Polarizing filters only allow light to enter the camera from one direction, thus negating the off-angle incident light and giving more vibrancy to the scene.

In the image below, sunlight creates a glare by reflecting off the leaves on the branch.  Using a polarizing filter, this glare is removed.  This technique has often improved the images I've taken, whether portrait or landscape shots.  Try one out yourself!