The best lectures I've seen have powerpoint & chalkboard, sometimes with an overhead projector. Each have their purpose.

1. For displaying text, graphics, animations, etc a powerpoint presentation is great.

2. The chalk board is great for pulling out important equations that will be used throughout the lecture (not lost on slide changes) and to interactively work through a problem. You can draw something out and then ask students what to do next and then execute.

3. Overhead slides are great to manipulations on complex forms. For instance showing how a parser works on a piece of text you can use a pen to mark up the text. Or to show how different actions can effect a system. For instance if we increase the interest rate, the line moves like this etc. This allows you to answer questions in real-time in a visual way.