Not an exhaustive list of hardware software, but most popular solutions in main areas of service infrastructure. Sort of like the SWITCH web page for video conferencing equipment, only for administrators and infrastructure, with proposed areas:

• SoftPBX (only ones tested by contributors - post feature matrix)
• Added services (for Video-conferencing, Instant messaging, Presence, Voicemail  etc.)
• Gateway hardware (recommendations)
• Clients (only widely available and recommended ones)

Post a feature and compatibility matrix