I see a lot of really pretty bracelets made out of cotton cord, with sliding knots. They seem to be really popular.
I have recently started using some cotton cord in my jewelry making, but I have never made a sliding knot. I ran across a very nice blog with a wonderful tutorial for making adjustable sliding knot bracelets "Art Bead Scene blog", and I thought maybe some of my readers would be interested in how to make a sliding knot. So if your interested you can find the link here at Art Bead Scene Blog.
Here's a couple more tutorials that might interest you.
Copper Wire Bead Bracelet