First you need a couple of strong characters. Finding one is already hard. Then they can't have any romantic feelings at all, which kind of cuts off all male-female couples, like Lafiel - Jinto from Seikai no series, even though noone would call it a romance. And I also prefer dynamic characters, so not one is in focus all the time.
Sakura - Tomoyo from Card Captor Sakura
Hikaru - Sai from Hikaru no Go
Youko - Rakushun (the rat) from Twelve Kingdoms
Tsubasa - Hikaru from Figure 17
Koichi - Coo from Kappa no Coo to Natsuyasumi
Alicia - Akari from Aria-series
Minori - Taiga from Toradora!
Kyon - Haruhi from Suzumiya Haruhi no Yuutsu
Yuzu - Kippei from Aishiteruze Baby
Murasaki - Shinkurou from Kurenai
Too lazy to comment each of them, its basically about the criterias I first listed about being two characters, both developed, and a dynamic interaction.