My solution is to use a tablet PC (the pen-enabled kind, not the modern entertainment tablets like the Ipad),hooked up to a data projector.

I have "lecture templates" which contain the copying intensive stuff (statements of theorems, definitions, graphs, complex diagrams) on the page, along with plenty of blank space for annotation. Those are on a website prior to the lecture. The students print them off at home, and bring them to class. I then annotate the lecture notes (using a pdf annotator and the tablet pen) and the students take notes as they wish.

This, I feel, combines the benefits of having some complex material prepared ahead of time with the benefits of having arguments, calculations etc. developed in real time, rather than canned in advance. So it avoids the canned slides-whizzing-by problem.

The only disadvantages I can see are the limitations of screen size. Sometimes nothing replaces the virtue of a big whiteboard, and having every part of a long development in front of your eyes all at once. In that case, I use a whiteboard.