I have no need for a case, as I prefer to read with only the e-reader in my hand.
But I do have a need for a cover, for protection while travelling. After a hunt around I've decided on this one (the Sony ones are an extortionate price) :
http://www.amazon.co.uk/gp/product/B005LUZGLM
It should arrive next week, I'll post my opinion once I receive it.