Saw Palmetto reduces DHT to a great degree. When DHT is low, libido is low and you're mre susceptible to gyno. Nettles lowers DHT but also lowers SHBG, so it's a better choice.
Due to all he positive literature on Flax seed oil, I used to recommend it, but I've since changed my stance. It's a phytoestrogen which removes androgens from the body and has been linked to prostate cancer -- once again proving that research studies only tell part of the story. It has been shown to reduce gyno that has already been formed though. (Maybe as a topical? Hmmm)