Tom Neville from Revolution watched the film at one point.In the episode "Clue", Tom compares John Sanborn to Travis Bickle of the film. Admittedly, it wasn't the best comparison. That's the downside of analogies...when you apply critical reasoning to an analogy, you can poke a lot of holes in it by pointing out the differences.
Travis' dad is George Bailey from It's a Wonderful Life.This is a rare example of a Wild Mass Guess that somebody outside TV Tropes has thought of: the film critic David Thomson wrote a novel called Suspects which drew imaginary connections between movie characters, and one of them was that little Tommy Bailey, one of George's sons, grew up, joined the military, served in Vietnam, was wounded and returned home, and the experience changed him so much that he changed his name from Tommy Bailey to Travis Bickle. George is basically an idealist who wants to do the right thing by people, but the endless frustrations of his life drive him to despair and thoughts of suicide, and it's only when the people in his small town rally around him and show him how much he's loved that he recovers his good humour and appetite for life. Travis is also an idealist and there are strong hints that he's a Midwesterner like George, but he has no real friends and he doesn't belong to a community. His frustrations drive him over the edge: he projects his own alienation onto the (admittedly very alienating) city around him, and in the end he chooses the target of his violence purely for reasons of opportunism. He can't get close enough to Palatine to kill him, so he goes after Sport instead, who doesn't have Secret Service protection.
The passenger who tells Travis that he wants to kill his wife doesn't existThis, like the above entry, has also been proposed elsewhere. It has been theorized that this character was imagined by Travis, and represents the deep recesses of his mind.