Recommendations may change a bit depending on your career goals. These are for the "armchair cardiologist," aka residents rotating through cardiology consults and the CCU.
Manual of Cardiovascular Medicine by Griffin is a good all around, quick reference at the resident and junior fellow level. Has chapters not only on disease entities but also for each cardiac procedure.
Hurst's Ventricular Electrocardiography is a quick read for ECG's. A web version used to exist. Not sure if it can be found now.
For a solid understanding of the structural basis for ECG's, consider Marriott's Practical Electrocardiography. A little lengthy, but no where near as long as Chou's text and far easier to digest. IMHO, the versions after Dr. Marriott stopped authoring them aren't as comprehensive.