Free.  Padlet is like a blank canvas in which students can brainstorm, use as collaborative notetaking, exit tickets, reflection, bell ringer, pre-assessment, summation tool and so much more.  Students can put any content (images, videos, documents, text) anywhere on the page.

$3.99.  Although a paid app, it is absolutely the BEST!  If you cannot do it with Explain Everything, it probably can't be done! Create slides using an infinite canvas, draw in any color, add shapes, text, math equations, videos, images and audio files.  Use a variety of import and export destinations including Evernote, Dropbox, Box, email, and more.  
 

Free.  ShowMe allows learners to turn their ipad into a personal interactive whiteboard.  In addition, ShowMe allows learners or teachers to record voice-over whiteboard tutorials and share them online.  Features include voice-record, entering text, importing pictures from photo library, or web image search, unlimited lesson length.  AN amazingly simple app.

Free.  Doceri is a screencast video app  that students can easily save and share to show what they know.   Teacher can also use this for flipped classrooms.    A highly rated app in the iTunes App Store.