There are many types, shapes, sizes and flavours of exhaust available. Most look much smarter and are lighter than the over-sized OE offerings. Unfortunately some pipes can actually rob you of a great deal of go. A lot of road legal pipes flow less than the standard pipe they replace and can have a surprisingly detrimental effect on power.
You may have also noticed that until the need for larger catalytic converters slung under the engine with trendy stubby exits, most pipes use similar length header pipes and have a similar overall tuned length. This is for good reason as a lot of after market under seat pipes and bolt on stubbies just don't work well with modern engines due to their larger degree of cam overlap. It is possible to run into real problems trying to cure flat spots and sort the fuelling with a poorly designed exhaust so choose carefully.
Yoshimura and Akrapovic systems and cans are examples of a good design, and whilst not being the cheapest, they are thoroughly dyno-developed and are well-built using quality materials. They also score high by having some of the best Power Commander maps already written for them. Definitely recommended.