Side Effects Software has released the 2014 Demo Reel featuring the work of Houdini customers worldwide.
Tea and Cookies in Houdini - Tutorial
Tea and Cookies in Houdini is a two part commercial tutorial in Houdini, going through all the steps of the scene's creation.
Houdini 13 Update
Side Effects's latest version of Houdini 13 comes with new particles, finite element solver, lighting workflow and more.
Houdini Geometry Tools
Diego Inácio has created several geometry tools for Houdini, using Python.