I'm another that can vouch for sex working....it didn't send me into hard labor but it did start me dilating both times and that's just as good if you ask me (the further you can be dilated to start off the labor the better IMO!
)
Let's see...other than the ones mentioned here already:
Black or blue Cohosh herbs (only under medical supervision though...)
Egg Plant Parmesan
A1 sauce and Mac n Cheese
Relaxation (to prevent adrenaline release in the body-which inhibits labor)
Some swear by mopping the floor (or any strenuous activity I guess)