Some shavers are especially designed for shaving body hair, while others are regular electric razors that are sold with body shaving attachements. The later are more versatile, but if body shaving is something you do on a regular basis, then you may want to opt for the former. Some of these body shavers have long handles that unfold, in order to help with those hard to reach spots on your back.
Body shaver pictured: Philips Norelco Qg3280/41 Multigroom Pro, Blue
Also of interest: Philips Norelco BG2040/34 Philips Norelco Bodygroom Pro Grooming System / Mangroomer Sku 211-6 Professional Do-it-yourself Electric Back Hair Shaver / Panasonic ES2207P Close Curves rechargeable Wet/Dry Ladies Shaver