Fat Quarter Shop has a free pattern for a really cute coffee koozie.
I've made several of these before, but I particularly like the way this one is sewn together. It is geared for the cute little 2 1/2" squares from mini charm packs. I had some leftover end pieces from another strip-pieced project that were perfect for this. You make two-patch units, then lay the first unit on the left end of a piece of batting, layer another one on top, right sides together, sew along the right side and press open. Continue with the rest of the two-patch units.
I'd love to show you this cute little koozie around my favorite coffee mug. I was sure I had taken a picture of it. Before I gifted it to a friend. Oops. (It makes a great gift!)