The humble dishcloth. You can never have too many. A quick project made with the simplest of materials and giving a satisfyingly practical reward.
The pattern says that it takes an hour to make up, but I have to confess it took me about 2 (with a few distractions). I used regular 1mm stationery string, which is 100% cotton, and a size 5mm hook. http://www.ravelry.com/patterns/library/diagonal-dishcloth-3.
I’ve only made one of these, but will make many more, I’m sure. Great to have cleaning cloths like these in all the bathrooms and kitchen sinks.