http://sebastianmarshall.com/ - Sebastian is my favorite writer. He generally discusses productivity, personal development, strategy (life and business), etc. Highly, highly recommended.
http://artofmanliness.com/ - The Art of Manliness is (as you would suspect), a site for men. It discusses things like: how to find your life's purpose, how to become a better man--generally stuff that isn't really discussed between men, but that men should know. They write long, well written articles that cover a lot of subjects.
http://www.stevepavlina.com/blog/ - Steve Pavlina is a controversial dude. He writes about personal development, but also tends to throw in vegan / spirituality type stuff every now and then (which I disagree with). Overall, his writing is very great. He does long-form pieces that fully discuss an argument, and it's worth reading along.
On a lighter note, I also try to write in a 'motivational' type style on my personal site, just in the off chance you're interested: http://rdegges.com/
There are tons of other blogs out there (The Art of Ass Kicking, etc.), but I generally find the other options to be too 'commercialized' for my liking, and they're filled with those really short, hyped up kinda articles.
yeah, the same here. I usually prefer authors who write for the sake of writing: the content is more "pure".
I second your recommendation on Sebastian's site. I'd add:
- Skinner Layne http://skinnerlayne.com/blog/ - Games and Strategy http://gamesnstrategy.blogspot.com/ (about strategy, lifehacks, history etc) - The Rationalist Conspiracy http://rationalconspiracy.com/ (For rationality stuff)