If all you want is a simple, privacy friendly login then check out Mozillas persona: https://login.persona.org/
Chances are your users won't have it already, but it's the only single sign-on solution I would use without calculating how much privacy I'm willing to "sell" for not having to register yet another time and remember yet another password.
Thanks! The Persona team is working hard to get past the "your users won't have it already" bit.
1. By the end of March, we'll turn on a Persona <-> Yahoo (OpenID) bridge, followed by one for Google (OpenID) and Hotmail (OAuth). Net win: A billion+ users can fully complete a first-time login with Persona using just three clicks. (Try it today! Use a Yahoo address at http://beta.123done.org/)
2. A subset of the team is working on a Persona-backed replacement for Firefox Sync. Net win: tens or hundreds of millions of additional users added to the "Persona-ready" camp.
3. The upcoming FirefoxOS phones all have Persona baked into the default Marketplace. Net win: time will only tell.
The above projects just streamline the initial onboarding experience: anyone can use Persona right now with any email address. FWIW, last time I checked, Persona's is averaging > 13,000 daily login transactions over a rolling 7-day window.
I don't want to derail, but if you have questions or need help getting Persona set up on your site, please free to email me.
Second that. Mozilla persona is fully distributed and not owned by a single entity. Moreover, it sounds like great engineering: do just one thing and do it well.
I hope it becomes the universal single sign on of the Web.
Chances are your users won't have it already, but it's the only single sign-on solution I would use without calculating how much privacy I'm willing to "sell" for not having to register yet another time and remember yet another password.