In the spirit of Best of RSS , podcasts , books I ask you :
What is the single best online article every programmer must read. The older the better (timeless factor) .
I will kick off the discussion with some of my favorites in the answers so you can vote for them independently of the question. As Joel suggested in the last podcast please provide one link per post so people can vote the answer they like up and the best links bubble to the top.
Ken Thompson's Reflections on Trusting Trust
Because of the insight that even if you have the source you can't easily trust anything.
Clay Shirky's A Group Is Its Own Worst Enemy
Because almost every programmer building social network seem to overlook the lessons in it. (I hope SO staff know better)
Joel's 12 Steps to Better Code
Because it is simple, effective and practical .
Fielding on REST:
http://www.ics.uci.edu/~fielding/pubs/dissertation/rest_arch_style.htm
It clearly lays out a rational alternative to SOAP--thereby proving that conventional wisdom isn't always the right answer.
One of my favourite articles is Why Johnny can't program by Dan Bricklin. It tries to explain what makes a programmer.
Everybody who has to give a crucial presentation to management should have a look at PowerPoint Does Rocket Science--and Better Techniques for Technical Reports.
I agree with previous commenters on Joel's articles.
Although I don't think this is the best article on programming, I don't think the list would be complete without Rob Pike's Notes on Programming in C.
I like algorithms, so I'm picking on the goodness of binary search by Tim Bray.
Teach Yourself Programming in 10 Years, by Peter Norvig (2001) as a realistic response to the idea you can do it in 21 days.
There is no single article that's going to give you all that much knowledge, far more valuable is how excited its going to get you about your chose career path. I love stuff by Steve Yegge. Not at all related to web development but his Execution In The Kingdom of Nouns had me running for the nearest compiler.
Guy Steele: Growing a Language (1999).
It's a transcript of his keynote talk at OOPSLA 1998 - video is also available.
I was re-reading Steve Yegge's The next Big Language , about JavaScript taking over the world, which sounded like an interesting speculation just 18 months ago, but now in light of all the progress made by Apple, Mozilla and Google it almost seems like a prophetic prediction :-)
Definitely an interesting read