David Richardson has created a multiple-part tutorial for modeling a mech in ZBrush.
Timelapse ZBrush Sculpt
Jose Alves da Silva has posted a timelapse of him sculpting a skull in ZBrush.
ZBrush SIGGRAPH 2013 Recap
Here is a massive recap of ZBrush's presentations from Siggraph 2013.
Eat 3D - ZBrush Hard Surface Techniques
Eat 3D have released a new video tutorial with instructor Mike Jensen, called ZBrush Hard Surface Techniques.