A case is definitely helpful to protect the Kindle, and I also find it makes it easier to read.

This is the one I use most often:
http://www.amazon.com/M-Edge-Jacket-...dp/B0025PH4HK/

It comes in a bunch of colors, but each is a different listing on Amazon, so do a search for "M-Edge GO! Jacket for 2nd Generation Kindle."

Whichever cover you get, I definitely recommend a cover with the Kindle hinge system on it instead of just the elastic corners. The device is much more stable in the cover, yet it's still easy to take on and off.