SynthEdit@groups.io - Discussion group for support, collaborating and bug-reports.
http://syntheditforum.boards.net/ SynthEdit Forum (message board).
KVR Modular Synthesis forum - Good general modular synth forum.
SynthEdit i Sverige - SynthEdit forum in Swedish.
nay-seven - SynthEdit forum in French.
SynthEdit @ DSP Central - A repository of all things created with and for SynthEdit.
syntheditusers.org - A collection of files and prefabs from the defunct SynthEdit Yahoo Group
https://syntheditstepbystep.wordpress.com/ - SynthEdit Tutorials by Cajhmere.
Quick-Start Guide to SynthEdit - At BIPTUNIA
Visual VST/i-Programming - A Comprehensive Guide to Creating VST-FX and Instruments with SynthEdit. E-Book by Peter Schoffhauzer, David Haupt, and H.G. Fortune.
Welsh's Synthesizer Cookbook - This book covers ground that is often left untouched by other synthesizer books and was written to fulfill the wishes voiced by synth programmers.
Becoming a Synthesizer Wizard: From Presets to Power User Covers learning synthesis with 4 modular environments, including SynthEdit. A little dated now.