Here are some hopefully interesting links on the Yubikey.  The last link is a walkthru as to how to use it with PAM. 

https://wiki.archlinux.org/index.php/Yubikey

https://www.yubico.com/applications/computer-login/linux/

http://m.linuxjournal.com/magazine/yubikey-one-time-password-authentication

http://blog.rootshell.be/2009/03/27/yubikey-authentication-on-linux/