Resources Concerning Potential Sponsored Partners
The U.K. Access Management Federation has an extensive list of Shibboleth-protected resources that are available to U.K. federation members. Since these vendors are already Shib-enabled, they may be more likely to join InCommon and work with you as a Sponsored Partner.
Also in the U.K., JISC maintains a list of publishers currently discussing federated access management, and their known status. This may be a resource to leverage for federating with InCommon.
The German federation lists all of its members, including vendors (note: this is in German)
SWITCH, the Swiss federation, lists its partners here:
SURFnet, the federation in the Netherlands, lists its partners here: