I have an Invisible Shield on my iPhone. I like it, but it was very difficult to apply, and I never did get the corners right so they look horrible now. Plus, the front seems to attract stickyness like nothing else I've used. It always feels icky, and I'm constantly cleaning it off.
For my Kindle 2, I picked up a
Gelaskins Bookshelf skin. It's really more of a sticker than a skin, but it's cute, the artwork is nice, it's easy to apply, and it provides the perfect amount of grippyness when holding the Kindle outside a case.