Incipio Feather is one of the lightest cases for the iPad 2. Measuring less than 1mm, this is basically a hard shell that only covers the back of the iPad. The case fits nicely and has cutouts for ports and buttons, including a hole at the back for camera.
The obvious disadvantage with this type of case is that the front face of the iPad is left exposed. It is available in five colors and comes with a free free screen protector along with a applicator card. Costs 35 dollars. [official product page]
Also check out: