Barbershops will be available in all major cities in WotLK. You will be able to change various character customization features for a fee (anywhere from 2 silver to several gold depending on what you are changing and your level).
There will be an Achievement linked with it called Shave and a Haircut worth five achievement points.
Here is a video, thanks to Beta player Penn, showing off the Barbershop interface and some of the existing options for an Undead male:
The brand new hairstyles and features are not yet implemented as of Live Beta Build 8634.
The currently planned changeable character customization attributes are:
See the Images tab for more details.