I rarely turn to CGI, because it's way over used. Besides, I prefer practical over CG. But when I do use CGI, I use a program called Blender 3D. It's not very easy to learn, and it took me about two years of on-and-off practice to learn the basics. It's that hard. But anyway, I really only use it for the videos below, but I very rarely will attempt motion tracking and placing CG objects into the scene. Oh, by the way, I suck at that. However, the videos are here for your enjoyment!
Doctor Who Fan-Made Intros of Mine.
Not all of them are on here, but you can check 'em out here: CLICK ME!!!!!