Viper and Crane are a perfect match.They seem to be very close in the Legends Of Awesomeness episodes and the Kung Fu Panda movies.
Crane and Viper are usually seen together, and they often cast glances in each other's directions.They work together quite well, and are always there for one another.
In the episode "My Mama Told Me Not To Kung Fu", Viper looked crushed when Crane announced he was leaving the Jade Palace.Also, in episode "Serpent's Tooth", Crane was one of the first to verbally stick up for Viper. Crane and Viper seem to be able to tell what each other are thinking as well. For instance, in Kung Fu Panda 2, when Viper notices a sheep being picked on by one of Lord Shen's wolves, Crane immediately picked up on her concern, as he asked Po if they could help the sheep.
In short, Crane and Viper are as much a cute couple as they are best friends.

Tigress and Po are perfect for each other. They have clear affections for one another, though they do sometimes have squabbles.Here are some of the main proof of their affections.
In the episode "Bad Po", the bad side of Po called Tigress "good looking" and had an apparent crush on her.The good side of Po also had a liking for Tigress as he said her fur was shiny and looked good.
In Kung Fu Panda 2, Tigress and Po both held paws when Tigress was injured.Also, Tigress because she did not want to see Po get killed, insisted he stay in the prison.
Tigress and Po both love each other, and have a close bond. They are a perfect match.