Been using this http://www.cleanyourcar.co.uk/washin.../prod_144.html for the last few years, one bottle lasts forever, you only need about the size of a 10p into a big bucket of water, foams up a treat and cleans well, also it is ph balanced meaning that when you wash the car on a hot day you wont get horrible white water marks over the windows and bodywork. It leaves a nice just polished finish aswell


EDIT: out of stock on that site but there are other sites online to order from.

Otherwise the meguiars range can be found in Halfords etc