Are there any good herbal medicines for chronic headaches?

Yes. Magnesium is a compound that can help with chronic headaches. Non herbal options: if your headaches are related to tension, chiropractic or osteopathic adjustments can provide significant relief. In some migraine sufferers, food reactions can be a significant trigger for the migraines (get rid of the food reaction, you get rid of the migraine).
Yes. There is some evidence that butterburr and riboflavin can decrease the severity and frequency of chronic headaches.