We don't think you should ever miss this slide from Tom Barret. It is one of the best ones available online that provides awesome tips on how teachers can use iPad in their classrooms.
The slideshow features 102 ways to use iPad in the classroom and these tips are relevant for all teachers regardless of the subject matter or content area they teach. Most of these tips if not all are accompanied by links to apps that you can download and use on your iPad, not all of the apps included are free but they are really great.
Here is the link to read and download it in Google Docs.