Headsets.com Busy Buddy:

Compatibility Warning: MAY NOT work with ANY Cisco EHS, Cisco SPA phones headset jack, or Marathon Partner Set-Up -- SET UP FIRST THEN TEST.
Power Source: Could use power cord or USB
Color: Red solid when on an active call, blue when we flip the switch for DND
Sensitivity:Dial is located on the left hand side of the box in adjustments are needed
Connection: RJ9
Setup: HDS Answers # 2106
Design: Top light in the 2nd picture (to the right)
Headsets.com Busy Beacon(DISCONTINUED) :

Compatibility Warning: MAY NOT work with ANY Cisco EHS / Plantronics EHS / Polycom EHS with VVX models / Marathon Partner Set-Up. Busy Beacon is an LED light so it might function and not burn out. Let our Customers know we guarantee compatibility.-- SET UP FIRST THEN TEST.
Power Source:Could use power cord or USB
Sensitivity: Dial is located on the left hand side of the box in adjustments are needed
Color: Red solid when on an active call, blue when we flip the switch for DND
Connection:RJ9
Setup: HDS Answers # 2106
Design: 1st picture to the right
Headsets.com Busy Light (DISCONTINUED!):
Compatibility Exceptions: Will not work with ANY Cisco EHS / Plantronics EHS / Marathon Partner Set-Up or Tel Wall Jack Set Up
Power Source: Power cord only
Sensitivity:Sound Sensitive (e.g. the light won't flash when the call is silent)
Color: Red bulb
Connection:RJ9
Setup: HDS Answers #332
Design: Top light in the 2nd picture (to the right)
Plantronics Online Indicator:
Compatibility: Wireless Plantronics units ONLY
Compatibility Exceptions: Will NOT work with older Plantronics EHS (ie. CS70/50/55 EHS)
Power Source:Piggybacks electricity from headset charging base
Sensitivity:Activation Sensitive (e.g. when the headset is on the light will always flash)
Color: urple light with red LEDs
Connection:3.5mm
Setup: HDS Answers # 287
Design: Bottom light in the 2nd pic to the right. The purple one :)