stunner, what year is that edition of Marion & Heald?
Here is a list of textbooks from Physics 401. (3) Electromagnetic Theory, University of British Columbia, Jess H. Brewer - and I'd have to agree in general with his assessments.
http://musr.physics.ubc.ca/~jess/p401/syll/2006/syll401-06.pdf
TEXTBOOK: David J. Griffiths, "Introduction to Electrodynamics", 3rd Ed.
(Prentice Hall 1999). ISBN: 0-13-805326-X
REFERENCES:
E.M. Purcell, "Electricity and Magnetism"
(slightly lower level than Griffiths, very nicely done).
Feynman, Leighton & Sands, "The Feynman Lectures on Physics", Vol. 2
(great book - a universal favourite of grad students studying for orals).
Corson & Lorraine, "Electromagnetic Fields and Waves"
(level similar to Griffiths but more "nuts & bolts").
Jerry B. Marion, "Classical Electromagnetic Radiation"
(level similar to Griffiths but emphasizing mathematical elegance).
J.D. Jackson, "Classical Electrodynamics" (if you want something to sink
your teeth into - graduate E&M - this is just a tad above our level).
L.D. Landau & E.M. Lifsh!tz, "Electrodynamics of Continuous Media"
(if you want to do it right the first time).
Arfken, "Mathematical Methods for Physicists" (great reference for
mathematics, vector calculus, differential equations, tensors, special
functions, coordinate systems, complex variable theory, Fourier analysis and
a wide variety of applications in all fields of physics, including E&M).
I used Lorraine and Corson - 30 years ago. Marion's books usually emphasize the mathematics, based on my copies of his Classical Dynamics.