Haemophilus - I have a few recommendations for you:
1. Saint-Francis Guide to Inpatient Medicine - This book is very easy to read and a good intro book for a medical student. Many medical students buy this book and with good reason.
2. Mass General Hospital Handbook of Internal Medicine - Can you really say anything negative about a book written by Harvard Internists for Harvard medical students and interns? Seriously though, the handbook is very concise and to the point. This book is probably more appropriate for a senior medical student.
3. Oxford Handbook of Clinical Medicine (American Edition) - I don't think many medical students use this book, but I thought it was excellent. I felt that it gave better explanations than the MGH handbook and was more comrehensive than the SF Guide. Oxford also covers basic General Surgery, Emergency Medicine, procedures, etc. However, the MGH handbook is thinner and more to the point. So, it really just depends on what your needs are. I would recommend taking a look at all of them at the bookstore prior to your purchase.
Other books to consider for your IM Rotation:
1. Mosby's Guide to Diagnostic and Laboratory Tests - I believe there is a handbook version as well. In Internal Medicine and in any other field, you will be ordering a bunch of tests. As a medical student, you will often not know why the heck the interns, residents, or attendings ordered a certain test or what the heck the test is to begin with. This book provides you with a test explanation, indications, critical values, test results and clinical significance, etc.
2. On Call Principles and Protocols - I never bought this book, but I've noticed one Medicine Intern and one medical student carrying it around when they are on call. I took a peek inside and it seems as if it would be useful when you are on call.
3. Maxwell Cards - For some reason, it seems like many medical students have these cards. I've always thought it was okay, but its usefulness is short-lived. I am somewhat suprised that someone hasn't come up with a better set of cards. Maybe I should come up with the Stinky Tofu Cards, I could probably make some money.
Freebie books:
1. Washington Manual
2. Pharmacopoeia
3. Sanford Guide
4. Pocket Doctor 2001
I've gotten several copies of these over the years because they are frequently given out by drug companies. If you know an intern or senior medical student, ask them to grab a copy for you. Everyone needs a copy of Pharmacopoeia and Sanford Guide. I rarely used the Washington Manual despite the fact that some swear by it. You can't really complain about free though.