Rex Flat Pedals (9/16")
These cheap and cheerful plastic pedals are surprisingly good. The large plastic surface is big enough to give some support, there are plastic studs for traction, and they're pretty light too.
Don't expect to replace the bearings when they're worn out, but they're comfortable and last longer than you'd think.
They have 3/16" pedal threads, which are the regular size for adult bikes.