Rotating face downwards I am trying to rotate a face downwards so that it looks like this:


I have not been able to do this by the R and any Shift+Z or X, Y or Y command. 
This is just a fake screenshot where I moved the vertices manually, to demonstrate what it should look like. 

Thank you.

I have uploaded the model here:
http://www.pasteall.org/blend/37734
Rotate using the 3D cursor as a pivot

With Shift+S you can snap the cursor to the geometry. Than set the Pivot to 3D cursor and rotate on the wanted axis.