depends on what you want to learn in zbrush. Alot of amazing classes and tutorials but they are usually for specific subjects unless you do the beginner classes. Beginner tutorials are good and cheap on digital tutors. High level classes and tutorials can be found everywhere but again, it depends on what you want to learn.…
There are a ton of tutorials on Zbrush's interface and what the buttons do but if you want to learn how to work efficiently, I highly recommend ravenslayer' videos, especially the long ones. There's surprisingly very little mucking about, the guy knows what is doing, for sure. A great watch :poly142:
A said above, there are so many good ones. I found the Eat3d Tutorial DVD's by Michael Pavlovic and Mike Jensen a tremendous help introducing me to zbrush and hard surface techniques, and they still garner a special spot in my Library. ..I should send these guys a cake or something.