Ouran High and the Special A.
A collaboration with each school to allow repairs to be done. It would be a year long school setting where each student would study at the other school while construction their school would be taking place.
I could see possibilities for a storyline crossover;
Jun Yamamoto and Tomaki Suou
over who's more dripping with good looks.
Kyoya and Hikari
A interest sparked by Kyoya to Hikari mainly because of her lively spirit.
Hikaru and Kaoru Hitachiin and Jun and Megumi Yamamoto
Both are acquaintance of each other due to their families careers.
Mitsukuni Haninozuka and Ryuu Tsuji
Budding interest in cutesy animals
Akira Toudou and "Mori" Morinozuka
Find out that Akira likes the strong silent type
Would just get along with everyone because she's more apathetic but tends to gravitate towards Kei Takishima only by his academic intelligence. This would be nothing involving a romantic relationship. However I could see Haruhi being obsessed over Tadashi Karino because of his cooking.
Anyways something like that.
Are you talking about what would be a good cross over, a specific one, or just ones you know of
my favorite crossovers are detective conan and magic kaito
Only one truth will prevail