Seth's Blog (http://sethgodin.typepad.com/)
Marketing Profs Daily Fix (http://www.mpdailyfix.com/)
Marketing Profs is the leading online marketing community with over 365,000 marketing professionals as members. It is a vast online resource with coverage of virtually any marketing topic imaginable. The Daily Fix is the blog of Marketing Profs and a wonderful resource in itself. There are over 100 contributing writers to the Marketing Profs blog, so you get authors who are really experts in their field. Unlike many multi-author blogs, they don't bombard you with new posts, there is an average of just one new post every business day. Recent posts have discussed the importance of marketing statistics, why most businesses fail with their websites, the importance of email marketing, measuring social media efforts, and business to business lead generation.
Duct Tape Marketing (http://www.ducttapemarketing.com/blog/)John Jantsch, author of the Duct Tape Marketing blog, has been called the world's most practical small business marketing expert. This blog is also one of my long time favorites; what I like is that Jantsch doesn't just review the latest marketing tools, he explains in detail how you can implement them in your business so they drive more sales. He is all about the application of new tools in the real world. He devotes many posts to helping readers understand how to use the latest marketing tools such as Twitter, Facebook, Google Analytics, and he also discusses the brand new marketing tools he has discovered that haven't yet become widely known. My only complaint about his blog is that it has a large number of ads, but you can avoid them by reading his posts through an RSS reader.
Sherpa Blog (http://sherpablog.marketingsherpa.com/)
Online Marketing Blog (http://www.toprankblog.com/)
The Online Marketing blog is from the people at TopRank, an online marketing and public relations firm. As the name implies, the focus here is purely on online marketing. They discuss search engine marketing, blogging, social media, online public relations and any other online marketing tool. The Online Marketing blog is not for the complete novice, but once you have the basics of online marketing mastered (by reading the other four blogs reviewed here), you will find some very useful tips here.