Forums:

Tracktion User Forum
Tracktion Support Forum
Multi-language Tracktion Support
K-v-R Forums
Cubase-Forum
Native Instruments Forum
Ableton Forum
FL Studio Forum
 (access only for FL users)

Company sites:

Raw Material Software
Mackie
K-v-R
Steinberg
Ableton
Apple
RME
Native Instruments
Spectrasonics
Propellerheads
Image Line/ FL Studio
WaveArts
Waves
TC Electronic
FXpansion

Product sites:

Tracktion
E-Phonic
Digitalfishphones
Greenmachine
Samplitude
Synthedit
Kjaerhus Audio
Simulanalog
SmartElectronix

Magazines:

Sound On Sound
Computer Music
Keyboards
Keys

Various:

Egle Vido
Egle Vido Mal- und Zeichenunterricht
Marcel Huber
Marie-Anne Vido
Christoph Frei