If you teach or have to make a lot of presentations, you can make your life a lot easier with an interactive whiteboard like a Smartboard. Instead of an expensive piece of technology, though, you can DIY it yourself with a Wiimote.
If you aren't familiar, a Smartboard is essentially a computer projected onto a touch screen. You can touch the screen to move forward a presentation, make annotations, highlight text, or do anything else. Obviously, they're pretty expensive.
DIYer Johnny Lee, however, realised that a Wii remote can track up to four different infrared signals at a time. So, if you were to mount a Wiimote near a projector, you could fake interacting with the screen using infrared pens. It's not the simplest project in the world—you'll need to do a bit of work to get it up and running, but it doesn't take too much specialised skill (like working with code or anything like that). All in all, it's definitely worth the time if you do a lot of presentations in the office. Check out the video to see a demonstration, and hit the link for instructions on how to set it up.