I'm not aware of such a list. However, perhaps the following can be the start of such a list that can be maintained by SearchSecurity. As usual, the listing here does not indicate endorsement and the list is in no particular order. Also, some companies provide full managed security services, while others provide only some managed services, such as managed firewalls.
For more information on this topic, visit these other SearchSecurity resources:
Best Web Links: Outsourcing
Security Policies Tip: How secure is your managed service provider?
The Information Architect: Oursourcing security a good plan, but be careful out there
This was first published in April 2002