There are several ways to do this:

Freestyle:

1. In edit mode, select all and press CtrlE> Mark Freestyle edge

2. Enable Freestyle in Render settings:
   

3. Enable Edge mark in Render layers > Freestyle line set > Edge types:
   

4. Render.

Wireframe material:

Another way is to use a wireframe material as described in this tutorial:

1. Add a material and select Wire, enable Z Transparency and set the Z offset up:
   

2. Add another material and assign it to all the faces.

3. Render: