It depends on what you mean by "impotence." If you have a medical condition that impedes blood flow (diabetes, for example) no home remedy will work. However, if you're having trouble getting and maintaining an erection due to aging, performance anxiety, or if you suffer from premature ejaculation, then it has been shown that some herbs could help.
According to The New York Times of January 1, 2008, "maca, a small root vegetable that grows in the central highlands of Peru, is known to impart energy, sex drive, and stamina. That view is supported by studies carried out at the International Potato Center, a Lima-based research center that is internationally financed and staffed. Studies there show that maca improves stamina, reduces the risk of prostate cancer, and increases the motility, volume, and quality of sperm. Some peer reviewed studies published in the journal Reproductive Biology and Endocrinology backed up those findings."
I've tried maca, which is contained in a herbal supplement called Zenerx and I thought that it did do something for me. It's more of a sex enhancer than a cure for impotence though.