Ivanko Supergripper

The Ivanko Supergripper is a nice grip device. There are certainly other ways to develop the grip
though. Kettlebells will develop a vise like grip, especially when doing the bottoms up exercises shown in The Russian Kettlebell Challenge. And you will be working a lot more than your grip at the same time. If you want to make an investment in equipment I would definitely go with kettlebells first and foremost. Dead lifts are also an excellent way to develop a powerful grip. See Power to the People for proper instruction in the dead lift.