I thought that a separate little computer - such as a bankcard terminal - could be connected via serial port and could use its own keypad and display to get transaction confirmation from user. Connected by serial (RS232) this is a low bandwidth connection that would isolate it from attacks on the network.
A bankcard terminal is merely a form factor for a small computer. A desktop appliance with minimal display and often printing ability. Many devices would fit this purpose at a low cost.
Actually...that's an interesting idea.
I've been working with a STM8S-DISCOVERY board to run
GNUK on the STM32 part. I still have some bugs to work out on the GnuPG implementation, but it may be interesting to try to hack up some code to make a smartcard-like application that can do transaction signing on said hardware. There is a bit of work that would need to be done on hardware as well as getting a client to be able to read the wallet from the hardware.
May be an interesting proof of concept.