I am not sure if you are looking for a carrying case or a everyday use case. So I will give both.
For the carrying case I use the incase neoprene sleeve. My sister has been using it for her white macbook for over two years and she loves it. I have only had it for about two weeks but I like it so far. I was trying to find a bookbag I like with a laptop sleeve but I was having trouble. So now I can use my favorite bookbag and the neoprene sleeve.
I almost always use the speck see-thru satin case in brick red and it has kept my unibody macbook scratch-free. I like it so much I am ordering the black version. I love the satin feel and that I can see the apple light up through the case.