I'm going through the AACNs critical care book now because I'm studying for my CCRN, but that would probably be a good one. Don't load yourself up too much with extra classes or training, you will get what you need in orientation. A lot of learning in the ICU takes place as you go, it's kind of hard to prepare for it ahead of time especially with no prior nursing experience. Be nervous, but be confident in yourself as well. I went straight into the ICU after graduation, and it's been hard been so worth it. Good luck!