About to start working on a social networking site, but I'd like to incorporate OpenID logins.
The JanRain plugin is packed in Debian, but seems flakey, and my brief interactions with it so far have not gone well. There's a bunch of others out there, but which ones are people using in production?
The OpenID Wiki has a great list of libraries available for PHP. Always begin your searches in the official documentation.
I have personally used and recommend EasyOpenId (requires PHP OpenID).
I've used the Zend_OpenID library from the Zend Framework and had good success with that. Very easy to setup and very easy to use. Their documentation on it is pretty extensive as well and comes with some good code samples that should show you everything you need to know. I used this briefly on one of my sites I was working on and only removed it because users didn't like OpenID in general. But the implementation was quick and easy.