A type 2 pinpad + openpgp smartcard might be the best practical thing right now -- a PIN on the card, plus a passphrase from the host (I think you can require both?). Type 3 showing a hash of what you sign, or a serial number of number of signs, would be even better.
The GPF cryptostick (usb) is also nice -- I think you could also take the Werner smartcard and cut it down to a smaller size for a USB stick sized reader. Sadly GPF stick 1.2 is out of stock everywhere.