You can start by checking out my Meta Guide webpages, “100 Best Animatronic Head Videos” [1], “100 Best Robot Head Videos” [2], “100 Best Hanson Robotics Videos” [3], and “Talking Heads (Draft)” [4].
There are two aspects to this project, internal and external. In fact, I usually recommend people create first a virtual talking head, for instance in a virtual world, such as Second Life. Second Life is really a great testbed for protoyping robots. A virtual prototype basically covers all of your internal workings. Later, you can apply the virtual prototype to an external or robotic talking head. For this, you can go with a generic robotic head, and simply dress it up after the fact as the character of your choice.
So-called rear projection talking heads seem to be the current favorite; however, there are also “virtual manequins” [5] available, though perhaps something of a compromise. To do this well is actually quite a big and potentially costly project; however, I believe that you can achieve satisfaction with just the virtual prototype phase, and get a much clearer picture of what you want and how to get there.
[1] http://www.meta-guide.com/home/talking-head/100-best-animatronic-head-videos
[2] http://www.meta-guide.com/home/talking-head/100-best-robot-head-videos
[3] http://www.meta-guide.com/home/about/videography/100-best-hanson-robotics-videos
[4] http://www.meta-guide.com/home/talking-head
[5] http://www.meta-guide.com/home/about/videography/best-virtual-mannequin-videos