I stumbled onto Purex Free and Clear over the summer. I bought it because it was cheap, it was a liquid, and had no dyes or fragrances. I tried it on my MF towels, and I really liked the results.
In fact, I like it so well that now I wash my clothes with the stuff. It is easily found at your local W-Mart.
However, I have some Der Wunder Wasche (Sonus), and I still use it to clean my PC pads. It does a super job. Pads have more gunk on them than towels, and I am surprised at how well Wunder Wasche cleans them out in a hot soak mode, with a bit of "massaging."
Haven't tried Charlie's Soap. Gee, time to spend more money on my "addiction." : )