This is a deliberately short list of organizations to look at. Wikipedia has a very good list of SDOs listing the formal international Standards Organizations. CEN has established a list of fora & consortia.
Copras is formally supported by the Information and Communication Technologies Standards Board (ICTSB). ICTSB itself has Members from Specification Developing Organizations. See the full list on ICTSB's website.
Note that there are literally hundreds of fora and consortia in the world. Not all of them do specification development. Some are more focused on marketing. The landscape changes daily. In September 2005, CEN has undertaken the laborious task of recensing most of them. The list of fora and consortia can be seen as a kind of snapshot.
The international standardization organizations mostly top a large regional structure. For reasons of maintainability and readability, you won't find a list here but only links to lists of those:
If there are any further suggestions, please contact Rigo Wenning