Ruben Mayor Senior FX TD of Sony Pictures Imageworks (http://www.aespid.com/) has released two very interesting tutorials on the world of Houdini.
Introduction to vex
introduction to vex, projects files:
www.aespid.com/index.php/tutorials/houdini-en/58-intro-vex-en
Intro to python in Houdini
projects files: www.aespid.com/index.php/tutorials/houdini-en/59-intro-hou-en