Game Maker is an easy to learn drag&drop programming language with lots of top end extensibility. It is suited for years 3 to 12. The unregistered version is a free download and has no time limitations. The registered version is 20 Euros with concessional pricing for site licences. It can be downloaded from http://www.yoyogames.com/gamemaker
Resources List
http://www.schoolgamemaker.rupert.id.au/
http://www.users.on.net/~billkerr/g/int.htm
http://www.mindtools.tased.edu.au/gamemaker
http://www.groups.edna.edu.au/course/view.php?id=81 teachers' forum
http://www.gamelearning.edu.au