Check this out!

A colleague sent me this link today. I haven't gone through it entirely, but at a glance it seems like an excellent source. It provides lists of apps broken down by tasks that you would like your students to complete. Have a look :)
http://edtechteacher.org/index.php/teaching-technology/mobile-technology-apps/ipad-as
For example, one table looks like this:

And there are 19 more!

FYI it also provides an opportunity for you to sign up for a monthly newsletter which could prove to be helpful.