Ask Slashdot: Open Hardware/Software-Based Security Token?

Qbertino (265505) writes I've been musing about a security setup to allow my coworkers/users access to files from the outside. I want security to be a little safer than pure key- or password-based SSH access, and some super-expensive RSA Token setup is out of question. I've been wondering whether there are any feasible and working FOSS and open hardware-based security token generator projects out there. It'd be best with ready-made server-side scripts/daemons. Perhaps something Arduino or Raspberry Pi based? Has anybody tried something like this? What are your experiences? What do you use? How would you attempt an open hardware FOSS solution to this problem?