Hi stuntdubl... online marketing is pretty broad, particularly if viewing from a general industry/market vantagepoint.
The fact that the Internet is still an infant when it comes to marketing standards, whether e-mail, web sites: portals, directories, auctions, and affiliates, off-line to online integration, promotions, sale conversions, branding, ethics and governance;
Also involved in online marketing is the art/science of Design: "navigation", "usuability", "channels and conflicts", "trust, security, privacy, and intellectual property"...
are some of the major topics, and these are still very broad.
Can you narrow this down?
Some other "my preferred" resources
Software Usability Research Lab
Dept of Psychology
Wichita State University
Updated November 5, 2002
Criteria for optimal web design [psychology.wichita.edu] (designing for usability)
Managing the Digital Enterprise
North Carolina State University by Professor Michael Rappa
Managing the Digital Enterprise is a guide to the challenges that face managers in the digital realm. Research papers and Case Studies on both sides of the discussions.
Digital Enterprise [digitalenterprise.org]
Not to forget WebmasterWorld itself.