The case I have for my 600 is a Tuff luv one I ordered from Amazon - I am very pleased with it, and they have also introduced one for the 650. Given that they have them for the 300, 505 and 700 as well as the Kindle 3 I'm guessing it's only a matter of time before the 350 version comes out - hopefully a link to the 300 version is attached
http://www.amazon.co.uk/Tuff-Luv-Sad...5270836&sr=8-5