Yucca looks like one powerful herb. It's quite cheap too.
http://www.ncbi.nlm....l=pubmed_docsum
http://www.ncbi.nlm....l=pubmed_docsum
http://www.ncbi.nlm....l=pubmed_docsum
http://www.ncbi.nlm....l=pubmed_docsum
http://www.ncbi.nlm....l=pubmed_docsum