Gemara

Honor of parents is compared to honor of Hash-m.

Kidushin 31b: When Rav Yosef would hear his mother's footsteps, he would say 'I will rise before the Divine Presence that is coming.'

(Beraisa): Fear of a parent is not sitting or standing in his father's place. Honor is giving him to eat and drink, clothing him, covering him, and transporting him.

33a: Abaye would rise as soon as he saw the ear of the donkey on which Rav Yosef (his Rebbi) used to ride.

33b: Rav Yehudah taught his father, yet Shmuel told Rav Yehudah to rise for his father.

(R. Eibo): A Chacham need not rise for his Rebbi more than twice a day, morning and evening, lest he honor his Rebbi more than he honors Hash-m (he says Shema Yisrael only twice a day).

Megilah 16b (Rabah): Learning Torah is greater than honoring parents. Yakov was punished for 22 years that he was away, but not for the 14 years that he learned in the academy of Ever.

Yoma 53a: When Rava would take leave of Rav Yosef, he would walk backwards until his legs hit the threshold. Rav Yosef's threshold became dirty with blood. When they told Rav Yosef (who was blind), he said 'may it be Hash-m's will that you become head of the entire district!'

Rishonim

Rif (Kidushin 13a), Rambam (Hilchos Mamrim 6:3) and Rosh (Kidushin 1:50): Fear of a parent is not standing or sitting in his father's place. Honor is giving him to eat and drink, and clothing him, from the father's money.

Tosfos (33b DH Ein): Only Talmidim learning in the Rebbi's house rise only twice a day. Others must rise even 100 times a day, lest someone see them and suspect them (of neglecting to rise).

Poskim

Shulchan Aruch (YD 240:1): One must be very careful about Kivud Av va'Em and fear of them.

Rema: In any case Beis Din does not force one about Mitzvos like this, i.e. an Aseh for which the reward is written next to the Mitzvah.

Shulchan Aruch (2): Fear is not to stand in his father's place among Chachamim with his friends or the place that his father normally prays, and not sit in his father's fixed place in the house.

Beis Yosef (DH v'Eizehu): One may stand where his father normally sits. This is no disgrace.

Taz (2): One may not stand or sit in his father's place even if he will not give any counsel or eat there.

Bedek ha'Bayis: Orchos Chayim brought a proof that he may not sit to his father's side without people in between.

Hagahos Tur ha'Shalem (4): His proof is from Shmuel 1:20:25. Rashi explains that David used to sit next to Sha'ul, and when David was absent Yehonason did not sit until Avner sat next to Sha'ul, for it is improper for a son to sit next to his father.

Shulchan Aruch (7): One must rise for his father.

Beis Yosef (DH v'Chayav): We learn from Rav Yosef, who rose for his mother, and from the Sugya of whether a son must rise for his father who is his Talmid.

Pischei Teshuvah (6): In Nachalas Tzvi (Otzar Meforshim 4) I proved that a Suma (blind person) need not rise for a Chacham of a Rebbi, unless he is Rabo Muvhak (his primary Rebbi). One must rise for a parent. This is unlike Be'er Heitev of Mahari Tiktin (244:1) citing the Posek Beis Hillel.

Note: Mahari Tiktin says that Beis Hillel.obligates a Suma to rise for a Chacham. Really, Beis Hillel obligates rising for a Suma Chacham.

Tzitz Eliezer (18:49 DH Shenis): The Birkei Yosef says that it is a Mitzvah to rise for a blind Chacham. Perach Shushan adds that this is because this endears Torah to those who learn it. If so, it is not letter of the law, and it does not apply to Kivud Av va'Em. However, presumably it is a Mitzvah to rise also for a blind parent, for their honor is equated to honor of Hash-m, and this endears this great Mitzvah to those who see it fulfilled.

Sha'ar Efrayim (78, cited in R. Akiva Eiger): We may learn from Yoma 53a: When Rava would take leave of Rav Yosef, he would walk backwards. I.e. he conducted with honor, even though Rav Yosef (who was blind) could not see it. However, Rav Yosef blessed him for this. If letter of the law he was obligated, why did he bless him? Perhaps it was because he walked backwards until he banged his legs. This much was not obligatory. We find that Abaye would rise for Rav Yosef. However, perhaps Rav Yosef was not blind at the time. (Note: see Ran Kidushin 13a, line 15/) Also, surely he acted beyond the letter of the law, for he would rise once he saw the ear of his donkey. Even though honor applies not in front of one's Rebbi, perhaps a Suma is different. The Shlah's son brought a proof from Yakov, who was punished for the 22 years he neglected Kivud Av va'Em, even though Yitzchak was blind. This was due to Kivud Em, for the Gemara mentions only his father! (Note: our text says Kivud Av va'Em). However, rising is due to fear of parents. We cannot learn from Kivud Av, i.e. giving him to eat and drink... Also, the Torah does not say that Yitzchak was (totally) blind, just that his eyes weakened. I bring a proof from Tosfos. Talmidim not learning in the Rebbi's house must rise whenever the Rebbi passes, lest someone see them and suspect them. One must rise for a blind Rebbi for the same reason. Even if letter of the law he is exempt, not everyone knows this, so there will be suspicion. Also, it is a disgrace if people see a Talmid not rise for his Rebbi.

Yechaveh Da'as (4:12 DH v'Emnam): Our custom is that after receiving an Aliyah l'Torah, a son kisses his father's hand, and a Talmid kisses his Rebbi's hand. Since Hash-m commanded to honor them, and their honor and awe is equated to that of Hash-m, it is a Mitzvah to honor them even in a Beis ha'Keneses. This is like we say (Bava Basra 119b) that one may honor a Talmid in front of his Rebbi if the Rebbi himself honors him. The Rashba (5:14) says that one rises for his father, Rebbi or Chacham even in a Beis ha'Keneses or Beis Medrash, even though one may not stand for others there. Ben Ish Chai (Vaykira 11) says that one kisses other relatives only if he is obligated to honor them.

Rema (8): If a father summonsed his son to a Din Torah, the son must go to his father's place, (even though normally the claimant goes to the defendant's place) even if he is in a different city, for this honors his father. The father must pay the expenses, for a son need not honor him from his own money.

Maharik (58, to a son whose mother summonsed him to Din): I decree that you go to her place. If someone else summonsed her to Din outside of her place, you would be obligated to go on behalf of her, to spare her the toil of leaving. All the more so, you may not burden her to come to you, and she will be disgraced in Beis Din! If this entails expenses above the cost of going to Din in your city, she will pay it. Perhaps really she is exempt, but I want that you have no excuse to refuse.

Gra (CM 14:19): The Rivash says that a son must be a Shali'ach for his father to claim from others to spare his father from disgrace.

Aruch ha'Shulchan (CM 14:4): A son (whose father summonsed him to a Din Torah) must go to his father's place, and a Talmid must go to the place of Rabo Muvhak. In other cases a defendant need not go to the claimant even if he must honor him, e.g. an older brother, father-in-law or grandfather. A parent is different, for Kivud Av va'Em is equated to Kavod Hash-m, and awe of Rabo should be like awe of Shamayim.

Shulchan Aruch (13): Learning Torah is greater than honoring parents.

Pischei Teshuvah (8): This is only if one needs to learn outside the city. If not, he serves his father and resumes learning.

Tzitz Eliezer (14:72:7): Since living in Eretz Yisrael is not a bodily obligation, like Maharitatz and Igros Moshe (EH 1:102) say, we can say that it does not override Kivud Av va'Em. One who continues to live in Chutz la'Aretz does not transgress. Therefore, we cannot learn from other Mitzvos that override Kivud Av va'Em. We can derive that other such Mitzvos (that are not absolute Chiyuvim) do not override Kivud Av va'Em, for their honor is equated to honor of Hash-m.

Rema (282:2): If one hears a Sefer Torah being carried, even if he does not see it, he must stand.

Gilyon Maharsha (240:6 and Gra 282:11): We learn from Rav Yosef (Kidushin 31b). This connotes that letter of the law, one must rise for his father when he hears him.