OneLogin is a cloud-based single sign-on solution that is pre-integrated with hundreds of popular web applications, such as Salesforce.com, Google Apps, Zoho, WebEx, GoToMeeting and Yammer.
SAML is used for the applications that support it while other sites use OpenID and API integration.
SaaS vendors are welcome to submit their own apps for integration for free here:
http://www.onelogin.com/vendor
OneLogin is pre-integrated hundreds of popular web applications
PingFederate is a standalone federated identity server utilizing SAML 1.0, 1.1 and 2.0 to enable secure single sign-on to Internet applications for employees, customers and business partners.