USMLE Step 1
Anatomy

Anatomy is about 15% of the test. There are a few very short and well
focused reviews that are definitely worth reading.

Gross anatomy: Reading your school textbooks won't take you very
far. The questions are very USMLE specific and very clinically oriented
(e.g. you have to know the anatomy behind rotator cuff injury, tennis
elbow, to recognize major structures on a CT scan etc). Read
High-Yield Gross Anatomy to understand and review these topics.

Neuroanatomy: it is well represented. And again very clinically
oriented. There are two review booklets that I liked and I recommend
that you read them both.
High-Yield Neuroanatomy is very well
structured and focused.
Clinical Neuroanatomy Made Ridiculously
Simple
has some additional clinical related material that I found useful
for Step1.

Embryology: very logical and easy to review. I believe BRS
Embryology
is the best book on the market. You could go over it in 2-3
days, and even it is a bit more than what you need, at least you make
sure you will get the embryology questions right.
High-Yield
Embryology
is a very short review of the information you find in BRS,
structured in the same way (the author is the same). If you feel like you
need color diagrams and some more explanations keep
Langman's
Medical Embryology
nearby.

Histology:
since most of the histology questions are in a diagram
format (e.g. you are asked to recognize structures on a micrograph or
diagram) it is useful to review a medium-size histology atlas such as
Wheater's Functional Histology.

Cell Biology:
I didn't feel very prepared in this area. There weren't
many questions either during the actual test. All I did was read
High-Yield Histology and Cell Biology, which although it is very
short and easy to read did not provide enough information.