The Turtles (inspired by the Logo[0] language I assume) in Computercraft[1] are really a lot of fun. Small 1x1x1 robots that fly around, dig, craft, place torches and all that fun stuff. Its using Lua as a scripting language with a very simple API[2]. I think its a great way to getting started with programming, you really have that immediate gratification when you see the turtle flying around and digging stuff up.

[0] http://en.wikipedia.org/wiki/Logo_programming_language [1] http://www.minecraftforum.net/topic/892282-145-computercraft... [2] http://computercraft.info/wiki/index.php?title=Turtle_%28API...