Hana Yori Dango and 1 Litre of Tears (for Japanese) was what hooked me, even though I'd watched quite a few before then.
A combination of It Started With a Kiss, Love Contract, Devil Beside You, and Mars (for Chinese/Taiwanese)
Full House, My Girl, and My Name is Kim Sam Soon (for Korean).
A fitting first post, I guess =) Though I feel old looking at the other responses here xD