I've been using this one since about two weeks after my K2 arrived:
Umbra Aquala Bathtub Caddy
Pros--I like it a lot better than the strictly wire ones; the wire arms are expandable to fit most tubs, there's a lovely cup holder.
Cons: I don't like the angle of the wire book rest, and it's not adjustable. This is a matter of preference rather than a design issue. It works fine, I just typically put my coated wire book rest on top of the unit instead as I have that adjusted to just where I like it.
I use this watertight pouch to keep the Kindle safe:
It's pretty sizeable compared to the Kindle, which allows room for both a cover and any silica gel packs you need. If you prefer a smaller case, TrendyDigital's model has also gotten good reviews here on the board.