Hello!
As a fellow upcoming 4th year...here's what I've heard from fellow residents for great books to carry along in your white coat
SubI --> Harriet Lane, Pediatrics On Call are both supposed to be awesome; i've heard having something like UpToDate can also be helpful, although personally, i don't really like Harriet. Some like Inpatient Pediatrics (The Philadelphia Guide) might be ok, but i've never seen it
Peds Heme/Onc --> Children's Hospital of Oakland Heme/Onc Handbook (Hastings), also the Peds Heme/Onc Secrets (Weiner) book is supposed to be OK (As a personal preference, I don't care for Secrets)
Peds Cards --> Pediatric Cardiology Handbook (Myung Park), & How to read Pediatric ECGs (also Park) are supposed to be a great tag-team
PICU --> Handbook of Pediatric Intensive Care (Pearson); I haven't heard too much on good handbooks for this one...
NICU --> Neonatology (Lange series, Gomella) is supposed to be great, also Manual of Neonatal Care (Cloherty)
Peds ID --> Access to RedBook, and DEFINITELY have the 2007 Sanford guide for Antibiotics
...Just what I've heard from various folks/faculty/IMHO
~Crazy