Below is a list of short (fewer than 1000 word) agile articles that substantially improved my understanding of agile. This list can be edited here: http://twtpick.in/56. At this link, articles can be upvoted, downvoted, and added. Over time, if you participate, this list might become something like a consensus view of great, short articles in the agile literature.
1. “This Is Not Like That” by Lyssa Adkins. Argues that agile concepts should be understood directly instead of by analogy. http://agileanarchy.wordpress.com/2009/12/18/this-is-not-like-that/
2. “Two Forgotten Agile Values: Discipline and Skill” by Brian Marick. Notes that team members often lack the skills they need. http://www.exampler.com/discipline-and-skill.html
3. “The Essence of Scrum” by Tobias Mayer. A contribution to the principle-centered view of Scrum. http://agilethinking.net/essence-of-scrum.html
4. “Agile: Is, Is Not, May Be” by Ron Jeffries. Takes a crystal clear position on the importance of developing software in every iteration. http://xprogramming.com/articles/jatagileisisnotmaybe/
5. “Flaccid Scrum” by Martin Fowler. Spurred the creation of Scrum developer certification programs. http://martinfowler.com/bliki/FlaccidScrum.html
6. “Measure UP” by Mary Poppendieck. Emphasizes the importance of measuring productivity at the team level. http://www.poppendieck.com/measureup.htm
7. “Escalation is Killing Agile — Can We Please Stop It?” by Jean Tabaka. A plea to reduce the violence in conversations about different ways to be agile. http://www.rallydev.com/agileblog/2009/10/escalation-is-killing-agile-can-we-please-stop-it/