Teaching Math in a PAPERLESS classroom. What apps should I use?

Next year I am moving to a classroom that can possibly be completely paperless.  The students get an iPad 2 and I can get any app that I want within reason.  Any suggestions for a good "book" for Math?

I have researched on my own and came up with a few apps that can be used to track improvement, learning, and anything else that will help stay paperless.

Khan Academy
Your Teacher
Allen Math
Algebra Boot Camp

Any others?

Surveys

Today Hannah asked about ways that students in America could take a survey and she could get the results back quickly.  I explained that there are websites that can do this for her quickly.  I also explained how to find ones in German for her own classmates to take.

American
http://www.zoomerang.com/

http://www.surveymonkey.com/

http://freeonlinesurveys.com/

German  (Hannah had problems finding websites in Germany that host surveys, so I found her this one.)

http://www.smart-survey.co.uk/