I have downloaded several hairstyle apps, for me this is one of the best.
Take a photo and try out several hairstyles,
This is not 100% realistic, but at least you can have a idea of final result.
The gallery of hairstyles is not huge, but have several hairstyles of each type: small, long, dark, blonde...
You have to adjust the hairstyle to your head manually, but it is easy to use.