Like for reference or to carry around with you? Honestly, a phone and the uptodate app or some other online reference (eg Peds in Review) works best for me. For NICU rotation, learn NRP and don't worry too much about it - honestly it's hard to read up beforehand for something like that. But since you asked, people have (and still recommend) Faranoff and Martin's 1900 page tome to me for neonatology and I promised myself I'd go through it at some point. It's a great exhaustive reference which I like using from time to time to gain an overview of the subject. Like, if you haven't done any ventilator stuff, sit down with a highlighter and read through their chapter on ventilation in babies. It's quite good.