[Very long hair]

Enigma Hair has ultra long (=ankle long) flexi hairstyles. They are pretty good, I´d say equally realistic as the avatars themselves are. But I think you should go see yourself.

[anyone know the best hair in sl?]

For me, Enigma Hair for ultra long flexi styles. I also like Truth and Analog Dog, but I roleplay and Enigma has the best collection of period styles.

[where can I buy realistic looking hair as all the hair I've seen doesn't move naturally...]

I also enjoy Enigma Hair's very long hairstyles. They are the best flexible long styles IMHO. Although they are not that realistic because of the prim limitations in SL, but that is something we must endure if we want flexible long styles.