Salesforce.com added SAML 2 support in the Winter 09 release a few months ago. This blog by Sun's Rajeev Angal explains how to configure OpenSSO for single sign-on to Salesforce.com using SAML 2.0.
Preview of OpenSSO's new OAuth Token Service. You can now use REST and the OAuth Token Service for securing your apps. It's a nice, light-weight alternative to WS-*.