how to toggle camera visibility?

I want to render a object that will have all necessary interactions like shadows and, specially, reflections, but I want that object not to be visible by camera. How can I do this?

I consider this to be an extremely important part of my workflow in other 3d suites. There must be a way to do that in blender.

For instance, I have an spherical object surrounding a reflective object. I want to render that object reflecting the other object, witch is between the object and the camera and after the object (the reflective object is inside it). How can I render the reflective object, reflecting all the spherical object it is inside, but that object not being visible by the camera?

Any way that I can think of, like putting th sky option, will make the reflective object not visible to the camera.