The stock seat sucks! That's the only thing that sucks about the bike. Some folks have bought airhawks, others have bought gel. I was just thinking to have the seat reupholstered. A few folks at work have used a company out of NJ, called Pirate Upholstery.
http://www.pirateupholstery.com/
They will ask you for your height, weight and other info like whether or not you have lower back issues or not. Then they customize the padding for you. Only issue for me, is my husband and I both ride the bike. So, I will probably need 2 seats or 2 RX3s lol.