Summer break is almost upon us and I want to use that time for some quality training. Can anyone recommend any training DVD's for either ZBrush or Maya?
You are asking two completely different modeling platform.
What do you want to focus on? Modeling Characters?
Maya or 3dsmax are the basis of all. If you can demonstrate that your model is rigorously good (polycount/uvw/excellent cut for joint deformation and animation) then you will able yourself to have a step in the door.
Zbrush or Mudbox are excellent hyper model detailing tools that are becoming in demand by professionals but low poly modeling is and will still be a requirement for Game Design for a very long time.
I would suggest to find tuts and focus on drawing concept then 3D model in Maya and set yourself with roughly 6000 polygons top.
Perhaps what is also best is find Zbrush tuts for baking, normal/displacement/occlusion. Export Zbrush and import in Maya for low polygon characters.
There are tons and tons of tutorials for both Zbrush and Maya that can be found online.
3Dcafe.com
3dlinks.com
Zbrush.com
Autodesk.com
these are very few links that can be interesting and .... free.