1) Goong (it is very long, but I recommend it; the art is nice)
http://www.mangago.me/read-manga/goong/
2) Model (I didn't read it till the end; but the plot and art are good)
http://www.mangago.me/read-manga/model/
3) Savage Garden (this is shoujo even if it has some shounen ai scenes in it but it is definitely shoujo)
Unusual plot & story - you should give it a try
http://www.mangago.me/read-manga/savage_garden/
4) Pink Lady (romance between two art students; highly recommended)
http://www.mangago.me/read-manga/pink_lady/
5) ANNARASUMANARA Manhwa (unusual art and plot)
http://www.mangago.me/read-manga/annarasumanara/
6) Akuma de Sourou manga
http://www.mangago.me/read-manga/akuma_de_sourou/
Do someone know a shoujo manga what is good an it should be a long manga
P.s thank you