Baskets are great for casual cyclists, who are wanting some extra room for their belongings. A lot of cyclists find them useful for carrying their handbags or shopping.
Although traditionally made from wicker, you can opt for a metal frame with a mesh basket bottom for something more sturdy. A downfall is that most of them will not offer any protection from the elements. If you commute in all-weather, you may want to consider a waterproof basket cover.