One of my favorite whiteboarding techniques in training happens to be the mindmap. I use them often and sometimes even indiscriminately. What I usually do, is get two whiteboards together and mindmap across the breadth of both boards. I do often get limited by the number of colours I have at my disposal - whiteboard markers seem to come in just 4 colours (red, blue, green, black), and my own artistic ability, though the sheer radiant nature of the maps more than makes up for it.
What I like about mindmapping in classroom situations is that it helps you retain the context of the current discussion and represents very clearly the chain of thought that the group followed through the session. They not only give you flexibility to adapt your session to the ongoing discussion in class, they also allow you to alter and add points in a flexible manner. The act of drawing up the mindmap itself is greatly enjoyable both for the audience and you as speaker (or so I think from my experience). As a side effect, it provides an instant takeaway for the group -- they can just click a picture and voila, you have session notes!
I think mindmaps are a really useful tool to have in your training inventory and I definitely recommend Tony Buzan's "The Mind Map Book" if you'd like to learn more about this wonderful technique.