ForScore is one of my very favorite iPad apps. It's a pdf reader with dozens of features aimed at performing musicians. I keep over a thousand scores–piano, flute, ukulele, teaching materials, etc.–in my ForScore library right on my iPad.
The ForScore 3.0 update adds many new features, but there are two that I'm most excited about because of their potential for classroom application.
Versions: A problem inherent in many iPad apps is that they are really intended for a single user. If one student annotates a score in ForScore, the annotation is permanent until another student changes or erases it. Sometimes this is cool, other times it's downright annoying. With the new Versions feature, you can save up to 24 versions of the same file. These are still linked to the one iPad, but with Bluetooth sharing and Dropbox support, you can send them to other devices as a 4SC file with annotations intact. I'm hoping for invisible cloud syncing at some point, but this is a great start!
Darkroom: I often take pictures of scores or teaching materials to keep in Evernote for quick reference (and to avoid carrying around that gargantuan songbook collection). Now I can use my iPad's built-in camera to take a photo directly into ForScore. These won't look as good as the ones I uploaded from my actual scanner, but they are usable and the process couldn't be quicker.
I'll let you know how it all works out in the classroom...