Official Training Videos
These tutorials cover most functionality of all plug-ins in the Trapcode Suite. They are warmly recommended for anyone who uses (or considers buying) the Trapcode Suite. View the Official Trapcode Suite training series by Peder Norrby.
More Training and Presets
The ShareLog area here at this site is a curated area where anyone can upload resources that are helpful for Trapcode users.
Or browse the ShareLog index by Tags and Title
And if that's not enough there are currently 99 videos in the Trapcode Tutorials channel on Vimeo!
External Training Resources
There are many sites that provide free training for Adobe After Effects and include some tutorials for Trapcode (and other softwares too). Here is an incomplete list of my favorite resources:
Red Giant TV (tutorials)
Red Giant People (presets)
All Bets Are Off
Ayato (English + Japanese)