Bill,
I have been using the Real Book and Gigit. The problem I found with Real Book is that once you scanned the music there is no way to edit. Gigit is an app that allows you to edit the lyrics.

Having said all that I have just moved into the OnSong app. Great, I can edit, change keys, use PDF files – and a bunch of other things. The set filling system is the best I have seen. You can even write yourself a note an place on your music in a different color so it stands out.

John C.