Probably the most unorthodox of the bunch on this one - but then I do only have a black edition A3!
I wash with (cold) water applied by a sponge with a bit of autoglam shampoo just to get all the dirt off, then use some nanowax spray and sham it off using an old towel (as I found chamois leather to be a pain... (takes so long to dry and wring out).
Have to say it does look very good once I've finished with it. Will only spend on more expensive products when I have a more expensive car!