Some Yorkie's ears won't come up on their own and need some help standing.
Shaving the hair off the ears to take some weight off is recommended. Sometimes the hair alone is enough to pull them down. If that doesn't help, here's two methods of taping them so they learn to stand:
http://www.shooterdog.com/alexfaq2.htm#EARS http://members.cox.net/jrogan/ears.html
But if you decide you like the floppy ear look, just leave it alone. They may stay floppy or they may come up on their own. I prefer erect ears, but there's a lot of memebers here with floppy eared Yorkies that are just adorable!