I've made some customizations to OpenID selector code ( http://code.google.com/p/openid-selector/) and combined it with MediaWiki OpenID extension, you can see the result here: http://www.sharingbuttons.org/Special:OpenIDLogin
Iwant to check it in back into the repository, but it uses "New BSD License" and I wonder if it's OK to do so.
Otherwise I'll write one from scratch and GPL it.
Sergey