I have a sizable collection of old terry cloth beach towels. Go to thrift stores or scavenge some, as I did. They work better than anything else, but it usually takes a bunch to get 'em really dry. I tried those super-soaker-upper-fake chamois towels, but they just aren't adequate for a Newf size dog. You would need two dozen to do the job.
We just use our old towels too! I've seen a couple of these 'super absorbent' towels advertised but I've only seen them in smaller sizes so not much use