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.

Source: https://technet.microsoft.com/library/security/dn903755.aspx