IDProxy.net
From the innovative mind of Simon Willison comes IDProxy:
idproxy.net, launched today, is my attempt at speeding up the process. It uses Yahoo!’s Browser-Based Authentication API to allow you to sign in with a Yahoo! account, then lets you create one or more OpenIDs (of the form
something.idproxy.net) to use with sites that support the OpenID standard.
Basically, it’s an OP that authenticates against Yahoo - call it an intermediate IdP, Proxy OpenID Provider, OpenID-Yahoo bridge, whatever.. it rocks!