I buy soft sponges at the dollar store, sometimes they have the sponges on a plastic stick like for washing glasses/bottles.
I find I get no marring, since they are 1 buck a dozen I throw them away after a few uses too. They really clean up well since they are coated in Eagle one wheel cleaner. I just bout 24 yesterday for 2 bucks, should last me through 2006
Around here they have the Megs brushes everywhere at half price, I even found some at Autozone for 4 bucks, this is the new type wheel and even the paint brush, personally I find both more harsh than the simple soft dollar store sponge. The bottle washer type allows me to get inside the wheel where the brush just cant reach.
The Megs brush seems designed for 18 wheeler rims, its just way too big and doesn't really work well for me with the 20 inch long heavy handle. I can see why they are being discontinued
Live and learn....