What is a good first-implementation for learning machine learning?
Decision tree. It is frequently used in classification tasks and has a lot of variants. Tom Mitchell's book is a good reference to implement it.
I find learning new topics comes best with an easy implementation to code to get the idea.  This is how I learned genetic algorithms and genetic programming.  What would be some good introductory programs to write to get started with machine learning?
Preferably, let any referenced resources be accessible online so the community can benefit