Hanuman and Bhima meeting is known to all, but some stories claim meeting of Hanuman with Arjuna even. The historical story of Hanuman in Mahabharata is not available in the book of Mahabharata or even in Bhagabat Purana. But Wikipedia claims that to be true. However, it depends on the readers how much trust they can put on Wikipedia regarding historical stories, putting aside Mahabharata and Purana. According to the story of Hanuman in Mahabharata, Arjuna reached Rameshwaram and there he exclaims why Lord Rama relied on the Banar sena for the bridge, when he could have built the same with his arrows. A monkey claims that an arrow bridge could not have carried the weight of the Banar Sena. Arjuna builds a bridge of arrow and the monkey with his pressure breaks it and challenges Arjuna, where ultimately Krishna intervenes and the monkey reveals its identity as Hanuman. Finally, Arjuna was given a boon to carry kapidhwaj flag on his chariot, where Hanuman will put the weight, so that the cart cannot be moved.
Marriage with Chitrangada was when Arjuna reached Manipur Palace. He found daughter of Chitravahana as wonderfully beautiful and falls in her love. Because of his handsome nature, the king allowed marriage of Chitrangada to Arjuna, but she lived in Manipur only. This was due to the wish of Draupadi, that she will remain the only wife of Pandavas in the palace of Indraprastha, as well as of Chitrvahana, since he had her as the only child. Later Arjuna visited five tanks of Manipur and rescues Varga. From Chitrangada, sprang one son for Arjuna, named Babrubahan. Afterwards in Mahabharata, a fierce battle took place between Arjuna and Babrubahan.
Ulupi was the second wife of Arjuna. She was affected by the beauty of Arjuna in Arjuna Vanavas Parva and took him to the deep water for a game. Arjuna refused her to marry in Mahabharata, when Ulupi asked for the same, stating that Draupadi claimed that no other wives of Pandavas must reside in Indraprastha Palace. However, Ulupi convinced Falguna that he can marry other ladies. The only thing he cannot do is to take them to the palace and she only wants a night from him. Thus was the marriage of Arjuna and Ulupi in Arjuna Vanavas Parva. All the things with life of Arjuna and Krishna happened with a different angle and these marriages too have such angles. From Ulupi, Arjuna got a child, named Iravan of great strength.
The sharing rule regarding Draupadi instigated Arjuna Vanvas, whose effect can be even found after the entire incidence of Mahabharata. Arjuna accepts and goes for a 12 year exile in this episode and that is directly linked with the sharing rule of Draupadi. Though, from no point of angle, arjuna should be guilty for his acts in this episode, still Arjuna blames himself for all and accepts the Arjuna Vanvas of 12 years. The episode is not having high level incidences, but it includes a high level of justice and morality, that can even frame an entire society. Importance of Arjuna Vanvas is not mere one though. In fact, the Chapter of Arjuna Vanavas Parva is the most important chapter in the entire book, as good effect of that is carried from 3200 BC till 500 BC in Indian History.