On her lovely RealMud Garden blog, Kati mentioned herbs that can act as oxytocin synergists. That is, these herbs may increase the effects of oxytocin in our systems.
She's talking specifically about blue cohosh and its use by herbalists to induce labor. (It's also a posible abortifacient.) But this info might be useful to those of us looking to boost our own, everyday supplies of the cuddle hormone.
I found an old newsgroup post by Michael Moore archived on Henriette's Herbal Homepage that recommends cotton root bark and shepherd's purse, as well as blue cohosh, as tonics that can boost those sweet oxytocin effects.