David Richardson has created a multiple-part tutorial for modeling a mech in ZBrush.
NanoTile Textures for ZBrush
NanoTile Textures is an unofficial plugin that helps create tiling textures using NanoMeshes in ZBrush.
Ben Mauro - ZBrush for Environments
Ben Mauro has released a free 3D environment design tutorial using ZBrush, Keyshot and Photoshop.
ZBrush SIGGRAPH 2013 Recap
Here is a massive recap of ZBrush's presentations from Siggraph 2013.