Being all about "zero budget" means educating yourself constantly...and thanks to the web you can do this for nicks. It can be hard to wade through WHAT is worth reading, but here's a few worth signing up for / following online.
http://www.clickz.com/: These newsletters are online marketing gold. If only I had time to read all of them, all of the time.
http://mashable.com/ : Mashable is the world's largest blog focused exclusively on Web 2.0 and Social Networking news.
http://www.ipsosmediact.com/knowledge/ : Ranking third worldwide in survey research turnover, Ipsos specialise in five areas of research: Advertising, Loyalty, Marketing, MediaCT, and Public Affairs. The online knowledge centre contains tonnes of info, case studies and free report summaries.
http://www.sendupalargerroom.com/ : Original marketing/consumer behavious Aussie blog by lead strategist for Carat Sydney.
(List inspired by article by Lee Stephens "Finding Gold Among the Spammers" from AdNews - 10 April, 2009)