I have a model which you can see here (camera perspective).
In the second image, you can see how the render turned out.
I'm at my wit's end trying to figure our why it's not showing up in the render. If anyone needs more information, just ask and I'll get it to you. I've already checked the normals and they're not the cause.
In object mode press W -> clear all restricted render. That will make all objects visible in the render. Also you can select and object and hit Ctrl+Alt+H to unrestrict render on the selected object. If there are objects that you have that you do not want rendered you can click the camera button next to the objects name in the outliner which is usually the top right window. This toggles camera visibility.
Version 2.80+ : Press F3 to bring in the search operator and type clear all restrict render.
Also check duplication setting of the object. I copied a part of existing mesh and separated the copied part to a new mesh. After doing this, Duplication setting for this new object was set to "Group". I changed it to "None" and the object finally appeared in rendered view.
Alternatively, next time you can check to see if anything has been disabled from being rendered. Just bring up the Outliner and look to see if the camera beside it is grayed out. I myself sometimes hit this by accident sometimes.
The shortcut to do this is Ctrl + H to turn rendering off.
Ctrl+Alt + H to turn it back on.
The other two are the eye and the cursor which means an object is invisible and disabled from being selected respectively.