The World Health Organisation (WHO) is a good place to start. It explains what swine flu is, has information on its prevention and treatment, as well as guidelines for individuals, communities and national authorities. It also has the latest updates and maps showing the spread of the virus.

The U.S. Centers for Disease Control and Prevention (CDC) also has a good in-depth section on swine flu.

ReliefWeb provides the latest information and updates from governments, regional bodies, aid agencies, WHO and other U.N. agencies.

The World Bank has a strategy to help countries fight swine flu with $500 million in fast disbursing funds.

The European Centre for Disease Prevention and Control focuses on the risks to Europe, and has some detailed information about the virus.

Finally, HealthMap gives an overview of the number of cases worldwide - but this is based on sources of varying reliability ranging from personal accounts to official alerts from organisations like the WHO.