One of my favorite tools is off-camera flash. Traditionally this meant large strobe lights, stands, cables, or expensive radio remotes in order to fire the flash. Today there is a large movement in the use of speedlights to accomplish the same results. Taking the flash off the camera allows for directional lighting and more dramatic appearance in the image. Of course there are numerous ways to accomplish this, but the Strobist site helps explain things and break it down.
The photo above shows one of my setups, which includes a light stand, Nikon SB-600 flash, and shoot-through umbrella. The SB-600 is a standard Nikon flash that can be mounted either on the camera or used off camera. The technology provides for the camera and the flash to “talk” with one another and achieve wireless flash synchronization. The advantage to the Strobist site there you can find a wealth of information on how to achieve this same result with very inexpensive equipment and what to look for when choosing your equipment.