Hi Rob,
You demoed a pedal that looked like a kick pedal in your video "MIDI Expression -- Pedal Sensing Technology". What was that pedal? It looked rugged and precise.
On cursory glance i found three 'kick pedals':
Roland FD-8, Price: $149.00
Roland KT-10, Price: $229.00
Yamaha KU100, Price: $70
Do electronic hi-hat pedals work? As for example the "Yamaha Electronic Hi-Hat Controller Pedal" ($90)
I'm also wondering about the Morley expression pedals, there's a ton of different ones. They look like they might be good. I thought the "Morley M2 Passive Expression Guitar Effects Pedal" ($54) like as found at
www.musiciansfriend.com might work.
Also in Expression pedals i saw the Behringer FCV100 ($30). the Moog EP-3 ($40), the Yamaha FC7 ($47), the Roland EV-5 ($60), and the Proline Standard Expression Pedal ($30). All are viewable at musiciansfriends too.
A list to start with doesn't need to be all inclusive and you can say that. Just a list of examples, that is added to when you're confident of a particular pedal or interface.
The note with that list that you aren't endorsing the quality or reliability of a particular pedal, just that it will work successfully with the Midi Expression seems appropriate too.