A new feature added to the developing Blender 2.5 allows you to easily display only renderable objects. This is very helpful when you want to isolate only those objects designated as renderable, or when you want to quickly hide things like the Grid, Cameras, Lamps, Empty objects, etc.
(You'll need a recent build of Blender 2.5. You can download the latest builds of Blender from graphicall.org.)
From within the 3D View,
press the N-key to display the Properties Panel.
Scroll down to the Display section
and enable the Only Render option.
You can control which objects are renderable by going to an Outliner view and toggling the "camera" icon to the right of the listed object. Of course, objects like the Camera, Lamps, etc. are non-renderable by default so no need to adjust their renderable option.