I just acquired my RX100 M3 yesterday. After researching online, it seems like among the better 3rd party cases are the Lowepro cases. Anyhow, today at Best Buy, I was looking at a few different options, including a hip case from Sony. I settled on the Lowepro Newton 30 belt case ($10.99). The Sony case was a very tight squeeze, and the other Lowepro Newton 10 case was scary tight ($9.99).
Anyhow, here are a few pics of the Newton 30 case with my RX100 M3..
[ATTACH alt="The Lowepro Newton 30 case. Measures about 6" length, and a hair over 2" wide with the camera in it. Best Buy had two colors available on the stripe, red or blue. I chose blue, to match my pants, and make it a bit more concealed. "]678524[/ATTACH]
The Lowepro Newton 30 case. Measures about 6" length, and a hair over 2" wide with the camera in it. Best Buy had two colors available on the stripe, red or blue. I chose blue, to match my pants, and make it a bit more concealed.

Here is a relative comparison of the sizes of the camera and case.

Inserting the camera, and removing it, is an easy affair with this case. The zippered top provides decent closure from the outside environment.

Nice and roomy on the inside. Even with this room, the case is nice and slim still, and there is room in the front zippered pocket for a memory card, cord, or something slim.

The case on my belt loop. Feels very comfortable, and is a slim fit. I like how the blue matches my pants, relatively speaking.
All in all, I am happy with this case. I am ordering a grip, and a leather stick-on decal for the camera for better grip. Cannot understand why Sony made this camera so slick, but I suspect its so that you could accessorize the camera to your style perhaps.