In the last issue of the Linux Journal, there is an article about the YubiKey. The YubiKey is providing One-Time-Passwords login, in a way Vasco and RSA do as well with their tokens. Although the YubiKey is working on (almost) any operating system (Linux/Mac/Windows/…).
It’s very easy to use, plug it in the USB-port and press the button. This will generates a 16bytes block. Together with the other open source tools of Yubico, you will be able to implement two-factor authentication.
So I will buy a YubiKey, to play around with