One of my favorites was applying the 30-day free trial to life habits: http://www.stevepavlina.com/blog/2005/04/30-days-to-success/
Also found his article on timeboxing useful.
More recently, posts like http://www.stevepavlina.com/blog/2008/05/how-to-be-a-man/ don't really ring as helpful to me:
2. Put your relationships second.
A man who claims his #1 commitment in life is his relationship partner (or his family) is either too dishonest or too weak to be trusted. His loyalties are misplaced. A man who values individuals above his own integrity is a wretch, not a free thinker.
Just not my flavor.
Also some totally insane nonsense on spirituality and enlightenment. Which is probably what happens to you if you make your career out of self-improvement.
The early articles are excellent, including the first article I ever saw describing what we would now call a conversion funnel (only it was for shareware)