When you buy a high-end DSLR, it usually includes a device called a hot shoe, which allows you to add all kinds of high-powered flashes. However, for mid-range DSLRs, pop-up flashes are generally installed, which greatly limits the flexibility of the flash. ExpoImaging's Rogue Safari Pop-Up Flash Booster adds a high-powered flash to cameras of this type, greatly increasing the range of the flash.
The booster clips right onto the pop-up flash, and it is able to increase the range by up to 8x, which ExpoImaging claims can increase the effective range of the flash by 60-70 feet (18-21 m). It is specifically made to work with lenses of 100 mm and greater.
The device isn't a flash itself, but is instead able to take the light produced by the pop-up flash and focus it, so it is able to provide light to objects over a greater distance. It doesn't require batteries, which should make it relatively easy to carry.
The Rogue Safari Pop-Up Flash Booster is available now directly from the manufacturer, for US$35. ExpoImaging offers a complete list of the DSLR cameras that will support the flash range extender.