My coworker Shawn introduced me to OpenID, an Internet solution that offers something similar to a single sign-on at work. It provides a framework for replacing logins and profiles for many sites with one centralized identity. The system itself is decentralized, though, so you can choose any identity server you want, or host your own.
You can now even use OpenID leave comments here! This uses the WordPress OpenID Plugin, which took a few tweaks to deal with having WordPress installed beyond the root of the website. I submitted a patch with my changes; if you’re impatient, you can just download my version. A diff is included for the curious.
To get an OpenID, there’s a long list of providers, or you can host your own server. I went with MyOpenID.com since the server had a lot of dependencies. Even with an outside provider, you can still use your own URL.
Update: Disabled the in-line sidebar/navigation login form, linked the OpenID text in the comments form.