Just released from Sher Music (publisher of some of our 'must-have' real books) is their Digital Real book series.
http://www.shermusic.com/digital_real_book.html
Their system works with Freehand systems' app for iPad (so no other music PDF viewing app is necessary.)

Note that our iReal book charts are not direct copies of Sher's real books, so you may need to create your own iReal book charts to match theirs if you are using our Player function with their charts.

(I have nothing to do with Sher music other than as an owner of many of their real books.)