Reading it opposite an unclothed person, Jewish or non-Jewish: Berachot 24a, 25b; Shabbat 150a
Reading it while one is unclothed, by keeping one's head beyond a divider between his head and his unclothed areas: Berachot 24b-25a, 25b; Succah 10b-11a
Reading it while unclothed, but with one's lower body submerged in clear/cloudy water: Berachot 22b, 25b
Reading it while one's foot is in contact with one's genitalia: Berachot 25b
Reading it in a "dirty" place: Berachot 24b; Rosh HaShanah 34b; Megillah 3a
Gaining a reward of long life for halting Shema while walking through a "dirty" place: Berachot 24b
Reading Shema opposite feces, if the feces is in one room and the person who is praying is in the next room: Berachot 25a; Eruvin 92b
Reading Shema near a chamber pot: Berachot 25b
What sort of covering for feces or over unclothed skin suffices to allow a person to recite Shema: Berachot 25b
Reading it while in bed with another person, or for a man to recite it while in bed with his wife: Berachot 24a