For a great overview of third year rotations, try:
• First Aid for the Wards

Differential Diagnosis Pocket Reference:
• Differential Diagnosis Pocket

Differential Diagnosis Reference:

• Current Medical Diagnosis & Treatment
• Common Medical Diagnosis: An Algorithmic Approach

Drug Pocket Reference:
• Pocket Pharmacopoeia
• Sanford Guide to Antimicrobial Therapy
• Drug Information Handbook 2006-2007

EKG Reference:
• Rapid Interpretation of EKGs
• EKG Pocket Survival Guide

General Pocket Reference:
• Maxwell's Quick Medical Reference
• Scut Monkey: Clinician's Pocket Reference
• Intern Pocket Survival Guide
• Medical Student's Pocket Reference
• Medical Spanish Pocket Plus

History & Physical Examination Pocket Reference:
• History & Physical Examination
• Bates' Pocket Guide to Physical Examination...
• How to be a Truly Excellent Junior Medical Student