The National Migraine Centre (formerly known as The City of London Migraine Clinic) is a charity with an excellent website with some very useful Fact Sheets you can print out:
http://www.nationalmigrainecentre.org.uk/about-headaches/fact-sheet/
Professor Muehberger’s site on Migraine Surgery has a lot of information too.
There is also The Migraine Trust and Migraine Action.