Search Engine Land - Eight Keyword Research Mistakes That Are Costing You Money

Excellent article on keyword selection. I especially liked the information about thinking like the search user, checking your competition and the competitiveness of keywords. You shouldn't rely only on keyword tools to make your decisions on the keyword phrases you use:
Eight Keyword Research Mistakes That Are Costing You Money

SEO Fast Start blog: Lies, Damn Lies, & SEO: Statistical Analysis of SERPs

Dan Thies debunks the myth of keyword density in an easy to understand post, its a good read:
Lies, Damn Lies, & SEO: Statistical Analysis of SERPs