LOOKING AT WOMEN
Gemara
(Rava): Iyov's mouth should be filled with dirt for saying "Bris Korati l'Einai u'Mah Esbonen Al Besulah." He credits himself for not looking at other women. Avraham did not even look at his own wife - "Hinei Na Yadati Ki Ishah Yefas Mar'eh At." This implies that until now, he did not know!
58a: R. Bana'ah found Eliezer (Avraham's slave) near Avraham's grave. Eliezer told him that Avraham was sleeping in Sarah's arms. R. Bana'ah asked him 'ask Avraham if I may enter.'
Avraham: He may enter. It is known that there is no Yetzer ha'Ra after death, so there is no need for modesty.
167b (Abaye): Even though a witness cannot retract his testimony after he testified, a Chacham normally is not so exacting about women, so he is believed to retract what he originally said (about a woman's identity).
168a (Abaye): When a Chacham goes to be Mekadesh a woman, he should take an ignoramus with him, lest they give to him a different woman at the Nisu'in. (The ignoramus would recognize that she is not the same woman.)
Kidushin 41a (Rav Yehudah): One may not be Mekadesh a woman without seeing her. Perhaps he will not like her appearance, and he will despise her, and transgress "v'Ohavta l'Re'acha Kamocha."
Avodah Zarah 20a (Beraisa): R. Gamliel was in Har ha'Bayis, and he saw a beautiful Nochris. He said "Mah Rabu Ma'asecha Hash-m";
When Turnusrufus' wife tried to seduce R. Akiva, he laughed, for he saw (through Ru'ach ha'Kodesh) that she would later convert and marry him. He cried due to her beauty, which would ultimately go to the grave.
Question (Beraisa): "V'Nishmarta mi'Kol Davar Ra" - one may not look at a beautiful woman, even if she is single, or at a married woman, even if she is ugly. One may not look at a woman's colored clothing, nor at animals or birds mating, even if they fill his field of vision, like the angel of death.
Answer: He saw her when he turned a corner. (He did not know in advance to close his eyes.)
(Rav Yehudah): One may not look at a woman's colored clothing even if it is on the wall.
(Rav Papa): The Beraisa forbids only if he knows whose clothing it is.
Support (Rava): The Beraisa says he may not look at a woman's colored clothing. It does not say 'at (women's) colored clothing.'
(Rav Chisda): It is forbidden only if she already wore the clothing, but not if it is new. If not, it would be forbidden to give new clothing to a professional to make alterations, for he will look at it!
Objection: Rav Yehudah taught that an animal breeder may insert the male's Ever into the female, even though one may not look at animals mating! You must say that one involved in his profession is not aroused to improper thoughts. This could also explain why we may give clothing to a professional!
Avos d'R. Noson (2:5): Iyov was stringent not to look at a virgin, even though he (some texts - or his son, brother or relative) could marry her, and all the more so at a married woman. He was stringent lest later someone else marry her, and Iyov will look at (Hagahos ha'Gra - think about) a married woman.
Rishonim
Rif and Rosh (Kidushin 16a and 2:1): One may not be Mekadesh a woman without seeing her. Perhaps he will not like her appearance, and he will despise her, and transgress "v'Ohavta l'Re'acha Kamocha"!
Rambam (Hilchos Ishus 3:19): It is improper to be Mekadesh a woman until he sees that she is pleasing to him, for if she is not, he will divorce her or cohabit with her even though he hates her.
Rambam (Hilchos Isurei Bi'ah 21:3): One may look at the face of a Penuyah (unmarried woman), whether or not she is a virgin, to check if she is pleasing in his eyes and he would like to marry her. There is no Isur. Further, it is proper to do so. He may not look lustfully. It says "Bris Korati l'Einai u'Mah Esbonen Al Besulah."
Ra'avad: The Gemara said that a Chacham who goes to be Mekadesh a woman should take an ignoramus with him, for a Chacham does not normally do so (look at them).
Magid Mishneh: This is not difficult for the Rambam. Even if a Chacham looks at a girl once, he would not know if they switched her, for he does not look at the form of women so much. An Am ha'Aretz will recognize her even if he saw her only once. If it were forbidden to look at a woman to inspect her, we would not tell an Am ha'Aretz to sin in order to help a Chacham! Rav Yehudah's teaching proves that it is permitted.
Yad Aharon (in Hagahos Tur ha'Shalem 8*): Perhaps the Am ha'Aretz will not lust, for he is like one engaged in his work. This is difficult.
Poskim
Shulchan Aruch (EH 21:3): One may look at a Penuyah, whether or not she is a virgin, to see if he wants to marry her. Further, it is proper to do so.
Beis Yosef (DH u'Mutar): The Magid Mishneh defended the Rambam well.
Nesivos Shabbos (in Hagahos Tur ha'Shalem 8): This implies that after the Shiduchin he may not look at her. A man may look at his wife when she is Nidah, for she will be permitted to him later. This is after they had Bi'ah, for then his Yetzer is not so great. Before Bi'ah, seclusion is forbidden; likewise, he may not look at her. We asked why R. Akiva looked at Turnusrufus' wife, even though he knew that later, she would marry him. We must say that before marrying her, the Yetzer is greater.
Note: One could say that the Gemara asked only about R. Gamliel! Also, perhaps after Shiduchin is more lenient, for he could have Nisu'in with her whenever he wants (when she is not Nidah)!
Taz (Kesav Yado 3*): Why didn't Avraham look at Sarah (before marrying her,) before he (accidentally) saw her on the way to Mitzrayim? The concern is lest he see something repilsive. Avraham resolved never to look at her, so there was no concern. This is why a Chacham should take an Am ha'Aretz with him to Shiduchin (the Chacham will never look at her). Iyov said that he did not look even at his own wife before marrying her.
Note: Rava holds that Iyov looked at his own wife. Perhaps Avraham saw Sarah before marrying her, but (until he saw her now) he assumed that her beauty faded due to travelling (see Rashi Bereishis 12:10)!
Ya'avetz (on Avos d'R. Noson): Why aren't we concerned lest Ploni look at her, another will marry her, and Ploni will look at her afterwards? If Ploni did not marry her, she was not pleasing in his eyes. Iyov was stringent, for he already had a wife. He could have looked for another wife, or a wife for his son or relative, but it is proper for one not to do so, lest he look at her after she is married.
Binyan Yehoshua (on Avos d'R. Noson): Ornaments are only for inside the house (Tanchuma Vayishlach 5), but not for Reshus ha'Rabim, because people look at her. We do not put a potential for sin in front of Kosher people, and all the more so in front of thieves!
Rema: Some say that one should not do with his wife matters of affection, e.g. for her to check his head for lice, in front of others.
Darchei Moshe (3): The Nimukei Yosef (31a, before the Mishnah): We learn from the episode with Avraham that it is improper to do such things with one's wife in front of others.
Rebuttal (Drishah 4): I say that only lying in her lap, like the episode with Avraham, is forbidden. Perhaps no one forbids perusing his head while he is sitting. However, the Rashba (1:188) compares this to pouring water on his hands and setting the bed, which are endearment.
Taz (1): R. Bena'ah was concerned for a lack of modesty for Avraham to lie in Sarah's lap in front of others, and also for perusing his head, lest it arouse desire in others. Avraham said that since there is no Bi'ah after death, neither is a problem. This shows that normally, one should not peruse her husband's head in front of others. This is only with a wife, for it makes others think about Bi'ah. One may peruse the head of her brother or father in front of others.