Just to add to the list, LightUp (http://light-up.co.uk) performs realtime Solar analysis all from inside SketchUp (in the same Window).
Here's a realtime capture of it in use comparing Summer and Winter insolation.
[flash=640,480:3897kuqs]http://www.youtube.com/v/jxPyMvI_EqI[/flash:3897kuqs]