While working on my iTunesU Anatomy course, I came across a great online science text. I am not usually a fan of textbooks, digital or hardcover, but this one was kind of cool. E. O. Wilson's Life on Earth was only $1.99 and had an entire section on the human body. The animations, specifically of the heart were some of the best I have seen.
I used Infuse Learning to create a few short quizzes over content I want them to understand from this book. They don't have an app that I could find so I just have my first period class type in the link to their website in Safari and have them create the shortcut. It makes it much faster for the other classes :)
What I loved about Infuse Learning is how easy it is to set up, access, and use in class. I also love that you can share with other teachers. You have the option of importing pictures too, which I use often.
*side note - My iTunesU course is a test right now. I am trying to see how it works and if its worthwhile to put all my information into one spot for students. I am about start the unit on the Cardiovascular System so that is the only one with much content at this time. It's a work in progress :)