Full disclosure: I stole the following idea from my wife.

For some courses, like calculus, I will create slides with beamer, leaving blank spots to fill in during class. I then print the slides out on paper and present them with the document camera during lecture. When I get to an example, I will work it out by writing on the paper during class, and have it projected in real time. This approach combines the advantages of blackboard talks where you work things out in realtime, with the advantages of beamer presentations where you can present nice graphics and also have an outline to limit getting distracted and wandering off on tangents.