I looked long and hard for a sturdy + grippy folding pedal. After some trial and error I gave up and bought the quick release MKS Promenade/Grip King pedals mentioned by the previous poster. Huge platform, good clearance, but one big disappointment -- with some shoes they were slippery when wet. BUT when modified with track shoe type pins they are fantastic. Carrying them separately is a small hassle but on the other hand the profile of the crank fitting is much smaller than a folded pedal. See the Rivendell site for guidance on adding pins. Rivendell also sells pins but any small track pins and some Loctite should work.
Ah so they have pin slots you can add to them? I'd need them because I'm usually wearing leather shoes with a flat sole so I like having pins, and a wider platform would be perfect. I don't mind carrying the pedals.
Thanks for all the replies!