Though it isn't specifically focused on portraiture, the
Sample Image thread offers several shots with technical info on each shot posted. You can select the type of camera, and lens used to show you what others have done with your equipment. You can check out other lenses as well to see if you'd like to try one out in the future.
Maybe one day they could add a filter to the search for the type of shot you are wanting to see as well, like Portraiture, Landscape, Macro, etc. Don't know how hard it would be to implement, but it would be very useful.