A quick list of some of my favorite marketing resources,

Marketingsherpa.com – One of the top research firms that track with is and is not working in all aspects of marketing. Well known for their charts of the week and whitepapers, their work is often cited by other top marketers.
marketingpilgrim.com – Stay current with the latest in online marketing news and developments.
Marketingprofs.com – Excellent marketing tools and advice for the marketing professional. Very timely and action oriented information that can be applied immediately to improve your success.
Quantcast.com – Especially their Media Planner tool, because you want to make the right media buying decisions based on vertical, demographics etc
Google Alerts – because you want to track what people are saying about your brand
pipl.com – A great way to do homework on prospects or clients.
ppchero.com – Learn potent pay-per-click strategies and tactics.
trendistic.com – Discover trends on Twitter.
Google Insight – With Google Insights for Search, you can compare search volume patterns across specific regions, categories, time frames and properties
sethgodin.typepad.com/seths_blog/ – Seth is one of the cornerstone conversation creators for the Marketing world. He is a best selling author and trend setting in the marketing world.
web-strategist.com/blog/ – Jeremiah Owyang is a Web Strategist. I will not go so far as to call him a futurist but he is on the cusp of emerging communications including social media and the impact to the individual and to society.
kaushik.net/avinash/ – Avinash Kaushik has built the seminal site on web analytics and understanding the intention buried in the data.
marketingcharts.com – Chats and data for markers in Web and Excel format.
econsultancy.com – Home of Rebecca Lieb – an accomplished and potent author of SEO books. The site provides expert advice on improving digital marketing and e-commerce.
webinknow.com– Online marketing and PR, an excellent resource where David Meerman Scott asks some of the most provocative questions in marketing today.
thefuturebuzz.com – Adam Singer talks about spreading buzz online for whatever you are doing.