Other examples of user-friendly OpenID login pages:

* Tripit.com only supports Google, Google Apps, and Facebook, but it's very end-user friendly to use any of those three.

* Catch.com, like Tripit, supports Google and Facebook OpenID logins.

* mindmeister.com supports Google, Google Apps, or a generic OpenID login.

* springnote.com supports a number of openID providers including generic OpenID. This one is actually an even better example than StackOverflow of an end-user friendly OpenID login/signup page.

Those are just ones I pulled from my Google account settings page. I'm sure there are other good examples out there.