It would help if you describe what you're looking for in a case!

Lightweight?
Strong protection?
Elegant look?

GumDrop is coming out with a durable, very strong case for the Transformer Prime in about a week, but it's rather expensive ($60)

However, it seems that it will make your TP bullet proof! Also comes with a plastic screen that overlays on top of the TP screen, for screen protection.

However, it's probably on the heavy side, and doesn't seem to have any built in stand.

Again.. without knowing what YOU are looking for, it's rather hard to give an answer.

 

I have found hte "MoKo(TM) Premium Quality Slim-Fit Folio Cover Case" to be nice quality leather and compact for the price. The TFP doesn't stay up in the angled positions as well as I'd hoped however. Doesn't close if you have the keyboard attached.

I would sure like to find a good compact case that is compatible with the keayboard and has nice leather and is still compact. I tried one from ebay that was horrible quality and smelled like a chemical factory!

 

i got the one they sold me at bestbuy when i bought the tfp. kind of like this one but for the tfp: Targus

 

I really, really enjoy the Minisuit I got from Amazon (where I also purchased my Prime & docking keyboard). Here's the item title, " MiniSuit ASUS Transformer Prime TF201 / TF700T Leather Keyboard Portfolio Stand Case Cover for TF201 Mobile Dock and Tablet (Brown) - LCD Cleaner Included". I'm sure you can find it easily doing a search on these terms if interested.

You just pop two snaps that are easily accessible and the tablet is quickly separated from the keyboard and just as simple to re-attach. It is made from beautiful leather (the brown goes very well with my 'purple' Prime) and there is no noticeable chemical odor. When all attached, I have had no problems with accessing the power, docking ports or cameras. I have only had mine for a little over a month and have by no means explored every need a user might have, but in my experience using it every day, in its suit, keyboard on, using the front-facing camera for Google Hangouts, I've had no problems whatsoever with the case. Also, the side of the folio that could hold a pad of paper is not only a good layer of protection but is also a very useful support for the screen, always holding it in place on my lap or a seat.

Jennifer