What is the best medicine to help people with chronic pain get some sleep at night?

Depends on diagnosis: The first and foremost issue is to have the correct diagnosis and figure out what type of pain exists. The best strategy to improve sleep is not necessarily a sleep medicine but rather a better control of the pain in the first place.

Long acting: Assuming that you have pain and that opioids are appropriate for you, a long acting medication (time release) will likely healp you to sleep better. These work by slowly releasing drug over 8-12 hours (or longer) rather than requiring you to take a pill every 4-6 hours.