Being a science geek - I use iSeismometer in my room. I show the app to the entire class using my document camera. We then play with moving the iPad to see how movement changes the screen. This is then related to earthquake waves.
I use a ring stand form the Science teacher as a mount for my iPad. I teach from it and turn on the camera if i need to show some documents.
To project, I either use a VGA cord with a 25 foot cord to the projector. This permits me to walk around. For apps, I use Splashtop and Reflector to project through the computer. Splashtop is a remote mouse for the desktop, while Reflector (cost money) mirrors my iPad onto the desktop which then projects the image.
Here is a link to apps I used when I taught a Presentation and Assessment class this summer.