While there are tons’ of limitations if you host your blog at wordpress.com, there are some really nice features as well.
One of these is Highlander Comments plugin: this addon extends your comment form with the possibility to use either your Facebook, Twitter or WordPress.com account for saying your manners. Being really jealous for this plugin, I started digging to search for solutions for self-hosted WordPress as well.

Social Connect plugin

The most complete alternative for Highlander is Social Connect plugin. It can provide login for Facebook, Twitter, Google, Yahoo! and WordPress.com. Quite easy to integrate, although Facebook and Twitter requires an application to be registered in order to use the connectivity.
Unfortunately at this very moment (2011.10.02) Social Connect plugin’s Twitter interface interferes with Flattr plugin but the others are working quite nice.

OpenID – a bunch of plugins

Social Connect uses both OAuth and OpenID as login possibilities. They are very different approach, and they are not for the same purpose. OpenID is a simple authentication protocoll, while OAuth is for authorizing an application to a profile or similar. Therefore OAuth requires applications to be set up on the other side and can provide a lot more than simple login and authentication. For those who does not want this process, a simple login with OpenID can be more than enough.

For this setup you’re going to need:

These three plugins can extend both login both commenting with the ease of OpenID. Google, Flickr (Yahoo), Verisign, WordPress.com, etc. are supported out of the box, but adding some more is not too complicated.

This three will add icon (or text) links for both login and comment forms, although self-setup login form will need an additional line inserted.

Other plugins

I’ve tried numerous other plugins but none of them was good enough for seamless user experience. Although I’m open to any better alternatives until Highlander is available for wordpress.org.