Best value for the money

I've seen attendings who have been out in the field for decades quietly slip this little gem from their pockets to get a quick peek. Not many pages, and each one stuffed with invaluable information. The only drawback is the small font size, with is a common problem for pocket references. I've just made sure I carry a pocket sized magnifying glass with me.

Essential

The most used book in my coat pocket. It didn't matter what rotation I was on this book is always in my coat pocket and is frequently used.

I also found this book to be pretty durable. I carried the same book in my pocket every day of my 3rd and 4th year of medical school and it is still holding up great through a lot of tough use.

Must have for M3 year!

If you buy one book to keep in your white coat, make it this one. For a small book that will easily fit into any pocket, it contains guidelines for writing admission, discharge, and other notes commonly encountered on medicine, surgery, and ob-gyn rotations. It also includes commonly used formulas and cheat sheets for H&Ps and the neuro and the minimental status exam.
A great deal for a book that you're likely to use through the rest of your medical training!