The U.S. Department of State provides information on each country including travel advisories, visa requirements, local laws, and much more. Be sure to check the 'Before You Go' tab as well as 'Country Information.'
The U.S. Centers for Disease Control and Prevention has information on specific health concerns in each contry on their 'Travelers' Health' page. Their website also contains a helpful disease directory.
TripPrep.com provides information on health risks and other safety considerations for 240 destinations as well as a 'Traveler Library' with information on illnesses and health and safety information.