Google supports HOTP-based codes that can be generated by a mobile application or even a local bookmarklet. They also support printed one-time codes. Here's th

Google supports HOTP-based codes that can be generated by a mobile application or even a local bookmarklet. They also support printed one-time codes. Here's the open source project for the mobile app and PAM module: http://code.google.com/p/google-authenticator/ http://code.google.com/p/google-authenticator/ (Disclaimer: I worked on this.)