I have tried loads of different things used to be Manager of Motaman in Bristol, so tried everything, Mer, Autoglym etc etc
But i used this the other day and its kicks the rest into touch :
http://www.meguiarsdirect.com/product_detail.asp?T1=MEG+G10810Comes out like a gel, as soon as i put it on my grey looking spoiler it stained it, soaked right in, done the whole car gave it a good long rub, buffed it off washed the car still looked great, best of all no streaks after the wash like Autoglym leaves.
I rate it 9/10 for application, 10/10 for non streaking, will have to wait to see how long it lasts though....
Jerry