My understanding is that evening primrose oil, semen, orgasm, nipple stimulation, etc. and so forth will help your body get ready but won't tip you over the edge if you're not ready.
Castor oil, on the other hand, can induce labor by causing contractions of the large intestine while your bowels empty, triggering contractions of the uterus. In other words, not a gentle method that will only help things along, but a real intervention and one that there are mixed feelings on (from my research). I wouldn't do this one myself unless I were facing a chemical induction in the hospital the next day. My friend did castor oil twice and regretted it both times after the fact, although it did trigger her labors.
Is this your first baby? You know that first babies are, on average, 8 days late, right? My baby was almost 2 weeks overdue, and it was really, really tough waiting, so I feel your pain. If it were me, I would definitely do the EPO/sex thing, try acupuncture/acupressure, but stay away from the cohoshes and castor oil.
Hang in there, your baby will come soon, when s/he's ready!