An artist from Brazil called Leonardo Davi published on his blog, a great collection of tutorials about sculpting with Blender. The tutorial was meant to be his final project, for a degree in visual arts.
In the tutorial he shows us how to model the head of a monster, in almost two hours of video. But, there is a down side in the tutorials, which is the audio narration. As you may be wondering, he is narrating all the steps of the tutorial in Brazilian Portuguese. So, if you don`t like the narration, turn down or off the sound for this videos.
You will find the videos (the tutorial has six parts) and all reference images here. The blog post, where Leonardo talks about the tutorials, can be reached here, and the text is in Brazilian Portuguese.