For me, it's gotta be:

- Harima/Eri from School Rumble - my absolute fav, just cus their chemistry together and Eri's my favorite character
- Koizumi/Otani from Lovely Complex - one of the first comedy romances I ever saw, still one of my favorite pairs
- Ko/Wakaba from Cross Game
- Ko/Aoba from Cross Game
- Midori/Seiji from Midori Days
- Nodame/Chiaki from Nodame Cantabile

are my favorites, off the top of my head. Cross Game was unusual for me cus I liked both of the main guy's love interests >.<

what about you guys?