Updated July 30, 2015
There is no way to see who views your profile on Facebook. There never has been, and there never will be. If that was possible, 90% of people would just completely stop using Facebook. In fact, most people do not even view profiles anymore, because everything they are interested in is already in their news feed on their home page.
Update: December 25, 2012:
Facebook changed the name of the ID for the routine that populates the chat box to "InitialChatFriendsList" to attempt to quell the FALSE INFORMATION going around that the routine which populates the chatbox (orderedfriends) is a list of people who view your profile. It's just a list of the people that populate your chat box. Anytime you see something that says viewing your own source code and looking for some numbers is a way to see who views your profile, you can be sure that it's just another hoax.
About Tracker Apps:
There is no way to create an app that shows you who views your profile, because facebook does not provide that information to app developers.... however, an app CAN see your friends list, and then just randomly select some people on your friends list to fool you, and lie to you, making you think it is working... but it's not actually showing you anything other than a random selection of a few of your friends.
Some people are under the impression that the "top friends" that display on your profile/timeline are the people who have viewed your profile, but this is not true. In fact, the opposite is actually true. Think of them like "suggested interaction" in the way that facebook has noticed that you might want to interact with that friend again soon.
Things that count as interaction:
• If YOU often view THEIR profile
• If YOU often search for them up
• If you have mutual friends
• If you have mutual games
• If there are private messages
• If there are timeline posts
• If there are mutual likes/comments
• If you view that person's profile