other Learning resources
CGWiki (tokeru.com/cgwiki)By far the best Learning Resource for Houdini. Written by Matt Estela. Completely free.
And the best - it's written, which is rare these days!
Houdini Masterclasses (www.youtube.com/user/houdini3d/masterclasses)Insight knowledge directly from SideFX. Always free. An absolute must.
Can be outdated though, so double check the Houdini version!
Applied Houdini (www.appliedhoudini.com)FX-heavy tutorials from senior ILM FX TD Steven Knipping. On the expensive side, but worth the money.
Entagma (www.entagma.com)A huge amount of tutorials. A bit of a mixed bag for me, since older Tutorials very much overcomplicated things unnecessarily. Choose carefully. Authors have a Motion-Design background, which is important to keep in mind.
CGForge (www.cgforge.com)Very good learning videos by Tyler Bay. A lot of free courses, a lot of paid courses.