(Photos: Picard)
Picard, a German toolmaking company, developed this clever design named the Lattenhammer. It's designed for those situations when you need to drive a nail, but you can't use a second hand to steady the nail. The nail slips into a groove in the top of the hammer. It's held in place magnetically. Once you've driven the nail in, it slips right out of the hammer, as you can see in this demonstration video.
-via Core77
http://jtc.net/hchc/nailer/
More specifically, Lee Valley carries one that uses a similar channel system with rare earth magnets to hold the nail in place for the first whack. It is THE BOMB for building temporary scaffolding. Yours for $40
http://www.leevalley.com/en/wood/page.aspx?p=32056&cat=1,53193
Look a nice enough hammer, The milled striking face is also used by Estwing and Stanley.