How about some face/wash cloths? These are great to scrub deep, but not abrasive against your skin:
The Circle Washcloth - looks like a lot of fun to knit!
Or some crochet scrubbies: UPDATED TO INCLUDE PATTERN LINK.
There are a million and one patterns you can find online (okay, I might be exgratting just a bit, but there are alot you can find!)
We also have a lot of other cotton yarns you can use for these projects or anything else you have in mind that cotton is great for.