I ordered a pair of Pedaling innovations Catalyst flat pedals - they are very long and designed so the pedal axel is in the middle of your foot. I haven't used them yet, but I've found a LOT of foot relief by riding with my mid-foot, even on flat pedals that aren't large enough to do that optimally.
Generally speaking, most flat pedals work for me, but on very long 100km+ rides, I get hot foot, general foot pain, and don't enjoy it as much as I should. I'm hoping the Catalyst pedals solve this problem.