Nick has mentioned the Natural Sea Sponge to me a while back and I completely forgot about it. Sounds intriguing.
Sea sponges are the best IMO, especially the wool sponge for extremely gentle washes. Just as soft as any mitt (once wet, not dry, don't let that deter you), will hold more solution, and will rinse free the worst grime with ease, even brake dust is released just by squeezing it a few times in rinse water. They can also be easily squeezed into tight spaces and you don't need to wash them when finished, just squeeze them out and let dry. I highly recommend them.
I bought mine locally, but, someone else had posted a link to these on amazon which are a better price - make sure it is at lease 8-9 inch sponge.
Amazon.com - The Natural Sea Sponge, 8 by 9-Inch, Wool - Cleaning Sponges