Beta Couple: Yi Jung and Ga Eul. They could also fit under Ensemble Darkhorse, considering the fact that there is probably more fanfiction written about them than about the two main leads.
Big Fancy House: There are several, predominantly Jun Pyo and Ji Hoo.
Bitch in Sheep's Clothing: Oh Min Ji, Jan Di's best friend at the High School. Lampshaded in that she gives Jan Di a stuffed sheep toy wearing the school uniform.
Jun Pyo: "If sorry was enough, then why would the law and police exist?"
Jae Kyung: "Let's go together!"
Cool Big Sis: Jun Hee, Jun Pyo's older sister who drives a white Ferrari and is known at school as "The Charisma Queen".
Dances and Balls: Several are showcased in the series, mostly set up by the school.
Did Not Do the Research: Jan Di takes pictures with a model, and then she's on the cover with the magazine with him the very next day. This leaves absolutely no time for photo selection, retouching, placement within the magazine, approval of the draft, printing, and distribution. That's a magical jenjang production process they've got going on.
Drowning My Sorrows: Jan Di accidently gets drunk, but still uses the situation to mumble her sorrow over Ji Hoo to Jun Pyo. YMMV, but this starts the transfer of her feelings to Jun Pyo.
Eiffel Tower Effect: Several important scenes are either at or within viewing distance of Namsan Tower in Seoul.
Multiple Choice Past: Is Woo Bin's family the mafia or involved in the construction business? Or both?
Nosebleed: Used in this series to indicate overwork and a general shutdown of the body. It mostly occurs with Jan Di when she is working more than two jobs.
Offscreen Teleportation: In episode 7, Jan Di on her bicycle chases Jun Pyo in the limousine, somehow arriving at the Shin Hwa residence at exactly the same time.
Ji Hoo's horse, given to him by Soo Jin, is named Rui after Hanazawa Rui who is Ji Hoo's counterpart in Hana Yori Dango
There Are No Adults: School children being bullied to suicide, burning bicycles and throwing trash into the school pool, kidnapping, blackmail, etc., yet no adults seem to exist on campus, and there are no consequences.
Triang Relations: Type 1, Type 3, Type 12, actually just about all of them at one time or another throughout the series.
Will Not Be a Victim: Jan Di tries to stand up for herself, even while physically being assaulted by groups of classmates.