In addition to the proprietary software that comes with each CBCT machine there are a number of excellent third-party DICOM readers available.  Choosing the correct software for you depends on how you plan to use it.  I have categorized the software below based on their target markets. 

Keep in mind though that most of these software are versatile enough be used for a number of tasks.  (For inclusion in this list the software must be able to import a DICOM for use in orthodontic or dental implant planning and be available for purchase independent of any hardware or services).

Click the links below to be directed to these 3rd party websites:

Software for Orthodontists:
Dolphin 3D by Dolphin Imaging
InVivoDental by Anatomage
Vworks by CyberMed
Quick Ceph Studio (Mac Compatible)
OnDemand3D by CyberMed
3DMDvultus by 3DMD
Dentofacial Planner by Dentofacial Software
SimPlant OMS by Materialise

Software for Implants:
SimPlant by Materialise
InVivoDental by Anatomage
coDiagnostiX by IVS Solutions AG
Procera Software Planning Program by Nobel Biocare
EasyGuide licensed to Keystone Dental by Anatomage
ImplantMaster by iDent
implant3D by med3D
OnDemand3D by CyberMed
Implant Location System by Tactile Technologies
Facilitate Pro by Astra Tech Dental
VIP Virtual Implant Placement Software by Implant Logic Systems
Blue Sky Plan by Blue Sky Bio

Software for Oral Surgeons:
Maxilim by Medicim
InVivoDental by Anatomage
3DMDvultus by 3DMD
SimPlant OMS by Materialise
Dentofacial Planner by Dentofacial Software

Software for Medical Professionals:
OsiriX (Mac Compatible)
amira by Visage Imaging
eFilm by Merge Healthcare
MedicView 3D Graphic Station by Medic Imaging
VolView by Kitware
Studio 11 by Geomagic
Vizua

Open Source Software:
SNAP (ITK)
ImageJ Volume Viewer

Am I missing a software?  Click here to tell me.  (Note: Before emailing me please double check to ensure that the software meets the requirements mentioned above).