Like this?
http://www.topeak.com/products/baskets/MTXBasketRear
If you get a rear basket, or front for that matter, I would recommend some kind of net to go over it and some bungees to help hold certain items in place that may require a little assistance. Wouldn't want to put something in your basket with no added protection, hit a bump, and your special purchase go flying in the road and smashed. What I like about Topeak racks is you can get a bunch of different packs, bags, and baskets to go with it so you do not need to change the rack or get anything special. I really like the idea of making a universal rack for all packs, bags, panniers and baskets. Really convenient and a breeze to switch out your carrier for different situations.