I have a silicone cover for my Kindle 1 from Vizu which I love and still use. They don't make them anymore.
I've been looking for one for my Kindle 2 and found
this. They're wicked expensive at $72.99 because they're sold in a 6 pack instead of just singles. I hope this will change.
Edit: I found they also sell them as singles for
$12.99. I'm placing my order. They are sold in other
configurations as well.