My first inspiration to grow my hair long came from Evanna Lynch, the Irish actress who played Luna Lovegood in the 5th Harry Potter film. Actually, I'm told I look very similar to Evanna. So, after hearing everyone comment on how I should dress up as her for Halloween, I had wished my hair was as long as her flowy classic length. Now, it's turned from wishing, to actually pursuing! I love the way her hair adds to her whimsical and unique personality, which is alot like my own.   Another inspiration came from another actress called Daryl Hannah, who I know best as Madison in "Splash". She plays a mermaid (one of my favorite mythical creatures) who has white blonde classic length hair.
This is Evanna Lynch:

And here's a link to a good picture of her hair:
http://lunafans.for-fan.org/gallery/displayimage.php?album=12&pos=20

This is my favorite picture of Daryl Hannah:

And this picture should give youa good idea of what her hair looked like in "Splash" (sorry if her bare bum offends anyone )
 

I think Evanna's hair was still that long in the film, but I wasn't able to find a good picture of it. If I remember correctly, her hair is flipped over her back for most of the film, so maybe thats why you didn't take too much notice of the length. I checked the screencaps of the movie on her official website, but there are none with just the back of her hair. I have heard that most of it was extensions, but she is now growing out her own hair for the next film, and apparently, it's pretty long now. So I think the photos I posted are of her real hair.