I've just got a blue one I picked up from Halfords I think. About 1/4 of the size of the bonnet and is just about perfect for the A3. I dry all the main panels with it and then use smaller MF cloths to clean the door shuts and get any little bits I missed.
I don't really buy into the £10 towel thing - I've just rinsed, very carefully washed the car, and then rinsed again: there shouldn't be any grit on it.
Using an open hose to sheet water off the car is brilliant, too - I hardly have any big clumps of water on the car when it comes to drying, just a light scattering of droplets which my smallish (apparently) towel has no trouble with whatsoever.