This is an addon script for Blender 2.78 and up which will generate a wedge mesh.
To install, download this repository or just the add_mesh_wedge_278.py file to your computer.
Click on File -> User Preferences, and select the Add-Ons tab at the top.
Click the Install from File... button at the bottom, select the add_mesh_wedge_278.py file, and click on the Install from File... button at the top of the dialog.
Once that's done, you should see the information for the addon in the window. Click on the square next to the name, and it's activated.
Don't forget to save your preferences if you want it to always activate with Blender.
In the 3D view, press Shift-A to bring up the primitives menu. Select Mesh, and look under the Monkey mesh to find Wedge.
Alternatively, you can also press Space and type in wedge in the text box provided.