Your bike seats constitute a major element of your riding comfort. It determines your posture, your position, style, and overall look of the bike. Most sport bikes have seats that aren't customizable. Cruiser and touring bikes have more flexibility in terms of being able to replace the factory installed seats with something that's more comfortable and fits your style.
Most motorcycle seats are made of genuine leather or high impact PVC vinyl. They're designed to withstand continuous stress, weather conditions and the elements.
Replacement seats can be obtained from most OEM shops and from 3rd party after market manufacturers. Popular brands include Corbin, Blitkried, Phantom, & Second Look. Bike seats with added passengers are also available.
Some things to consider when buying your replacement seat is: Material, Ergonomics, and comfort.