UK Professional Cartoonists Organisation (the PCO). This is the membership organisation which funds and runs the Bloghorn.
Cartoonists Club of Great Britain. A social club for cartoonists, pros and not-quite pros.
British Cartoon Archive - at the University of Kent. Find the history of UK cartoons and cartoonists there.
British Cartoon Museum. The central London home of things cartoon.
UK Political Cartoon Gallery. The central London home of things political cartoon.
US National Cartoonists Society. Some good friends from across the Atlantic.
Federation of Cartoonists Organisations (FECO). Some good friends from across the channel.