Unfortunately (I'm a kindle lover too!) the best books on Zen are either out of print completely or not available digitally :( Here's a couple of good lists thought:
Given the context of this discussion, I would recommend reading Charlotte Joko Beck's books. Specifically Nothing Special, which is available digitally on Amazon :)
I caved and ended up buying BOTH Buddhism Without Beliefs and Nothing Special. I got Nothing Special for $4 (used/paperback) so I figured I'll just throw it in.
Looking forward to some reading!