I have been teaching my 9-year-old nephew programming for about 8 weeks using Scratch (from MIT), a free system built on Squeak. It is a great system, very engaging and fun, and a good place to start before moving up to more sophisticated systems. My plan is to graduate him out of Scratch into either Alice or Lego Mindstorms, with possibly scripting in Smalltalk when he gets a little older.
I am very much bought into the teaching philosophies supported by Scratch and Alice--particularly that learning program ought to be more about learning core computer concepts and problem solving than worry about syntax. These visual systems do this quite well and I would recommend them even for adults--particularly those new to computers--before moving into traditional languages where you can quickly get frustrated by the syntax well before you learn the concepts.
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I am very much bought into the teaching philosophies supported by Scratch and Alice--particularly that learning program ought to be more about learning core computer concepts and problem solving than worry about syntax. These visual systems do this quite well and I would recommend them even for adults--particularly those new to computers--before moving into traditional languages where you can quickly get frustrated by the syntax well before you learn the concepts.