This is pretty anecdotal and I doubt there will be a list of names written down somewhere. However have a look at the number of acknowledgements in Microsoft's security bulletins from last year:
Palo Alto Networks - 34
Qihoo/360 - 27
FireEye - 14
Tencent - 14
Trend Micro - 12
Fortinet - 7
McAfee - 2
VMware - 2
Kaspersky - 1
They are a pretty unsavory company but they really know what they are doing.
The problem is that, more often than not when something related to Qihoo gets posted on HN the replies were invariably about how evil Qihoo is as a company. The discussion quickly becomes derailed and meaningless as the choir busily preach its own members.
Palo Alto Networks - 34
Qihoo/360 - 27
FireEye - 14
Tencent - 14
Trend Micro - 12
Fortinet - 7
McAfee - 2
VMware - 2
Kaspersky - 1
They are a pretty unsavory company but they really know what they are doing.
Source: https://technet.microsoft.com/library/security/dn903755.aspx