Canon produce their own range of lens cases which are well built and provide essential protection of your lens if it is lose in your camera system bag.
Lowepro has a large range of quality lens cases which are well built and provide essential protection of your lens if it is lose in your camera system bag.
Olympus produce their own range of lens cases which are well built and provide essential protection of your lens if it is lose in your camera system bag.
Sigma produce a range of lens cases which are well padded and designed specifically for each lens. They provide essential protection when carrying your lens around when it is off you camera.