The one friendship that stands out as significant in the text is the one shared by Jim and Huck.
When Huck finds out that Jim has been sold by the Duke and the King, he sits down to think through the problem. His solution, ultimately, is determined by his sense of friendship. Huck is caught between two conflicting moral mandates.
Society tells him that helping Jim to escape captivity is tantamount to stealing, as Jim technically is the property of Miss Watson. Huck believes that breaking the law by helping Jim to escape will lead him to "go to hell", yet Huck cannot shake his sense of fidelity. His other moral impulse is to stand by Jim because Jim had stood by him.
Huck reflects on the kind treatment he received from Jim along their journey down the river. He also remembers that Jim told him that Huck is now his only friend.
Huck demonstrates a considerable degree of loyalty throughout the novel, even with regards to the King and the Duke, and he continues in this moral strain when he decides that Jim's friendship is more important that damnation or any law.
The friendship that Jim and Huck share is real, more real than arbitrary rules. The morality that Huck ultimately alights upon is also more real than the morality of the majority, because it is based on actual people in actual circumstances, not on concepts and abstractions.