Besides the Fields text (which is probably too much for an undergraduate
course) there are three books that I have used to some degree for a 400
level (junior-senior) course.
"Medical Virology (Fourth Edition)" by White and Fenner
"Virology (Third Edition)" by Levy, Fraenkel-Conrat and Owens
"The Biology of Viruses" by Bruce Voyles
Each has it strengths and weaknesses. Quite frankly, none of them alone
serves the pruposes of a molecular approach to virology. White and
Fenner, of course, focus on human viruses and is limited in its
molecular information. Levey et al. takes a very classical (by the
families) track and includes reasonable molecular biology. Voyles has
the most unique approach in that he follows the events in the virus
life cycle and draws examples from different viruses in the context of
each step (e.g., attachment and penetration, genome expression, etc.).
I don't consider Voyles book to be at a very sophisticated level in
terms of molecular biology, however.
I hope this helps.
Department of Molecular and Cellular Biology
University of Arizona