The Khilafah is the state of the Ummah (islamic community)
There are numerous websites about the Khilafah
www.islamic-state.org/khilafah
www.khilafah.org
www.khilafah.com
www.geocities.com/harkatulkhilafah
www.hizb-ut-tahrir.org/english/english.html
www.ramadhan.org/1421/
http://www-personal.umich.edu/~luqman/
They even got a site here in the Netherlands:
http://www.expliciet.nl/
It contains also some links to international Khilafah movements. http://www-personal.umich.edu/~luqman/Belief/Khilafah/partI.html
Khilafah is the political system in Islam. It is responsible for implementing the Islamic system (be it social, economic, educational, foreign policy,...) and maintaining its implementation. It is also responsible for spreading the message of Islam to the world. Khilafah is the Islamic state which the Prophet (pbuh) sought to create and worked for in Mecca, for a period of thirteen years, until he (pbuh) established it Medina.
If you read some of the stuff on their sites, you can realize these people are dangerous and organized.
Also a while ago there was a picture of a European islamic cleric. On the background there was the black Khilafah flag.
A view on Jews and Israel from Khilafah.com
Also the www.muslimstudent.org.uk site is down, but here are two documents that were on their site:
Also look at reply #9 for another 'leaflet' of that same site. TopQuark posted it as a seperate thread, but I can't find it anymore.