The best SEO/SEM info (crowd sourced)

I’m rebuilding my blog from scratch so wondered what other geeks thought was the best information about SEO/SEM. You know, the techniques you can use to make sure your blog or website appears as high up in Google as absolutely possible? So, I asked on Twitter and friendfeed and this is what happened. Funny that a Google employee answered the question within seconds of me posting it. Thanks to everyone for the help, does anyone else have any other sites/sources to add?