Yubikey - http://www.yubico.com/yubikey - Check out the Github repo for the PAM https://github.com/Yubico/yubico-pam#readme -- Stop by and see me (Nick @ MNX Solutions) at Indiana Linux Fest http://www.indianalinux.org/ we have a few Yubikeys we are giving away.
Duo Security - http://www.duosecurity.com - These guys are doing some neat things in this area: https://github.com/duosecurity/duo_unix
Yubikey - http://www.yubico.com/yubikey - Check out the Github repo for the PAM https://github.com/Yubico/yubico-pam#readme -- Stop by and see me (Nick @ MNX Solutions) at Indiana Linux Fest http://www.indianalinux.org/ we have a few Yubikeys we are giving away.
Duo Security - http://www.duosecurity.com - These guys are doing some neat things in this area: https://github.com/duosecurity/duo_unix