There are few things I think set a bike apart like some great pipes. Aside from making your presence known on the road, they can change a stock bike into something really personal. Of course our friends at Stocks Harley Davidson can show you a ton of different looks, but if you're interested in learning a little before you talk to them, I thought this link was really helpful.
Personally, I like long pipes that push off the end of the bike if you're just looking to kill time by looking at pipes you I tend to look at the Vance and Hines site. Here is the link for the Harley pipes, and they've also got some videos like the one below.