9. Search Engine Land

Search Engine Land is a news and information site covering search engine marketing, searching issues and the search engine industry. The site is led by veteran journalist Danny Sullivan, formerly affiliated with Search Engine Watch.
Specifically, the paid-search column is an excellent place to learn paid-search strategies, as well as a way to get insight on many tricky paid-search issues like bid management, landing pages, tracking issues, quality score considerations and a whole lot more.