Have you ever uninstalled an app because you felt it's icon was too ugly to be seen on your screen? I know I have (I'm looking at you Mass Effect Infiltrator). The app icon, while often an afterthought during development, is one of the most visible elements of any application. It literally just sits there, exposed, 100% of the time you have the app installed. Make it look good, don't just phone it in.
While surfing around looking for inspiration I ran into this amazing app icon which looks like a hyper-realistic sunny-side-up egg. How badly I wish that icon was on my iPhone right now. Unfortunately, this delicious icon (especially in the morning hours) doesn't belong to an actual application, it is only a designer's flight of fancy. Maybe someday... But for now, there is an entire subculture of artists designing app icons just for the sake of it! Practice I suppose.
Some of these icons are made for actual apps, some of them are just for fun. All of them are works of art and deserve to be seen. They are presented in no particular order. If you find a beautiful icon that didn't make the list let us know in the comment section.