Excellent iPad Apps for Demonstrating Learning for Students

Reflector is software our school purchased a couple years ago for every teacher's work station. Reflector allows the user to mirror the iPad screen to a computer, which can then be projected onto the smartboard. Anything happening on the iPad, including animation and sound, is played on the computer screen as well. Now untethered from the computer, the teacher is free to place himself or herself strategically in the classroom.
Here are three recommended apps that would work well for using the iPad for modeling and shared demonstration:
1. Math Board ($5): Teach students how to work problems for the four basic operations.
From the App Store description:
"More than just standard drills, MathBoard encourages students to actually solve problems, and not just guess at answers. This is done by providing multiple answer styles, as well as a scratchboard area where problems can be worked out by hand. Students can also turn to MathBoard's Problem Solver for further help. This powerful teaching feature walks students through the steps required to solve addition, subtraction, multiplication, and division equations."
There is also Math Board Fractions and Math Board Challenge, a head-to-head game where two students compete to see who can complete the problems faster.
2. Notability ($6): This handwriting and drawing tool is considered an "Essential" by Apple. Using a stylus, a teacher can model how to closely read text on a PDF or screenshot, demonstrate with students a genre of writing, and show students how to organize data for a science activity. Pictures and audio recording of your explanations can be embedded into the document. Hand off the iPad to another students when they are ready to share their own work.
3. Popplet ($5): This app allows you to create idea webs, especially helpful when brainstorming ideas for writing or for pre-assessing background knowledge on a topic.
From the App Store Description:
"Popplet is the simplest tool to capture and organize your ideas. With Popplet you can quick jot down your ideas and sort them visually. Popplet is great for school and for learning in the classroom and at home. Students use Popplet to think and learn visually. By capturing facts, thoughts, and images, students learn to create relationships between them and generate new ideas. "
Which app(s) do you find useful for modeling and demonstrating with students on the iPad? Please share in the comments.