Medaka Kurokami is the perfect honour student. She has exemplary grades, talent at any sport she tries her hand at, comes from a rich family, is exceptionally popular, and has just become the first ever freshman student to be elected School President! During her inauguration speech she proclaims that she will endeavour to help every student with any problem if they simply submit it to the newly instated suggestion box. But with a bare-bones student council consisting of only herself and her unwilling accomplice Zenkichi, people are unsure whether to take her seriously or not. Regardless, Medaka takes each suggestion and gives her all to fulfil any request, be it ridding the kendo hall of delinquents, writing a love letter, or helping a struggling art student find his muse.
Both are mangas in which selfish, arrogant and talented female lead tries to change the world in some way. Her methods are weird, her actions are bizarre but the outcome is usually good. There is also a poor male character, who have a crush on the heroine. He is constantly getting abused and dragged around at girl's pace in order to help with the peculiar plans. Also on a course of story a lot of other weird characters gather around the girl, and aid her in her actions.
Both are mainly comedy, with some romance mixed in (and battles in Medaka case). If you like the treatment Kyon is getting from Haruhi, you will also like Medaka+ Hitoyoshi combi)
On a side note - Haruhi have anime way better than the manga, so if you decided to check Haruhi after reading Medaka you might consider watching the anime instead ( 2006, not 2009 though. 2009 is an abomination due to "Endless 8")
Ouran High School is a prestigious private academy where money and status count for everything. Haruhi Fujioka is a scholarship student at the elite school, and is appalled by the lazy attitude of the rich and powerful students towards their studies. The Host Club is a clear example of this: a group of six attractive and wealthy boys spend their time entertaining the female pupils for a profit. When Haruhi accidentally breaks a ¥8,000,000 vase belonging to the club, they force her to work off her debt as one of the club's members; and to do so, she must masquerade as a boy! Can Haruhi keep her gender a secret from the club's exclusive clients?
In the Melancholy of Haruhi Suzumiya and Ouran High School Host Club the characters learn that something outside of their own ‘world’ exists. In the case of Ouran they learn about instant coffee, which does not seem like a big deal to the average person but to the elite, aristocratic characters it was a major point in the series. Where as in the Melancholy of Haruhi Suzumiya, Kyon learns of aliens, time traveling, and espers, something the average person has no idea about. There is a little bit of romance squeezed into each series with some comical aspects too.