Best iPod/iPhone app for nursing school?

I just bought an iPod Touch and am loving it so far. I am starting nursing school next month and want to install an all-in-one app that will help while I'm at clinicals. I can't seem to decide between Epocrates, Skyscape Constellation, and Unbound Nursing Companion.

I am required to buy a lab & diagnostics book, and it's recommended that I get a drug guide and a medical encyclopedia. I'd love to take care of all three on my iPod so I'm not carrying a bunch of books around. Unbound allows access to books on my PC as well, which is a selling point. Skyscape seems to be less expensive. Epocrates seems to be really popular with nurses who are out in the field. I would like something simple to use, hopefully with cross referencing (which all three seem to have).

Any thoughts or suggestions?