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Your desire to work universially with the cameras of your students is a tough one, and the "smart" optical slaves mentioned above sounds like it may fill the bill, so I would look in to those.
If you just want a camera and flash combination, with out the common use by others, the Canon G series cameras like the G12 and G15 have a hot shoe on them that works with the full line of Canon flash units, including some fairly small ones like the 270EXII. The 270EX is pretty small and portable compared to full sized flashes, and it does allow bounce flash when mounted directly on the camera. You could also combine a short or long sync cord with the 270EX to get it off camera and maintain full ETTL or Manual flash contol, but that would be only one flash, not a second off camera flash. Plus of course the cord gets awkward, but it does prevent interference from other flashes.