A mounted flash unit provides more power and versatility than the pop-up flash that your dSLR came with, but it may not be performing exactly the way you had in mind if you're still craving a more intense flash or perhaps catching some red-eye effect in your pictures. As an alternative to the mounted flash, a hammerhead flash may be worth considering if the mounted flash isn't producing the pictures you want.
Among photographers, a hammerhead flash is synonymous with a Metz flash. They're the same type of flash, but Metz happens to be the most notable manufacturer of hammerhead flashes (although they make other types) so most photographers will use the terms interchangeably. The hammerhead flash sits off to the side from the camera body and is mounted by a bracket that connects to the camera (the bracket connects to the camera via the same screw hole that you would connect a tripod). Most of the brackets have a slit along the center so that you can slide the camera closer or further from the flash, although if you're going to use a hammerhead flash it's better to keep the camera as far from flash bulb as possible. The hammerhead flash syncs to the camera through a PC cable that you plug into a hot shoe adapter. A nice perk of using a Metz flash is that it will work with any camera type so long as you have the appropriate hot shoe adapter. While this camera/flash equipment is a highly professional outfit, it can feel a bit unwieldy at first due to its size and weight. If you take photos for an extended period of time using this outfit, expect your arms to feel sore the next day.
It goes without saying that this is a heavy duty flash that can withstand intense and rapid photoshoots. Even at full power, Metz flashes can have a recycle time - the time a flash a must "recharge" before it's ready to fire again - of two to three seconds whereas a mounted flash unit can take anywhere from six to ten seconds before they're ready to fire again. Metz flashes have such a resilient recycle time because it has a strong, dedicated battery capable of re-energizing it quicker. This powerful battery is also the reason a Metz flash can be used for much longer times than mounted flash units.