While it is probably the simplest way to use the iPad in the classroom, today I used the iPad as a reader. We needed to review some trigonometry in my calculus classes, and our textbook does not have a good trig review. So, I found a great pdf file online that I linked from my website. Students were then able to access the 17 - page pdf (which had great pictures and examples) without my needed to print and copy all of those pages!
Students enjoyed being able to zoom in on different parts of the pdf. And the best part: students were focused on the lesson, not distracted by having the internet and iPad applications in front of them!