VPO software
Samplesets (free)
List of samplesets on GrandOrgues Sourceforge page
Jeux d'orgues
Appletonaudio (also has free software for Noise Reduction and Looping of samples)
DIY related links
Vidar Fagerjord's webpage
Raphi Giangiulio's Homemade Pipe Organ (check especially under "Construction")
MIDI hardware