Ruling leniently on issues of mourning in general: Eruvin 46a-b; Moed Katan 18a, 19b, 20a, 22a
During the 2nd week, the mourner leaves his house but he doesn't sit in his usual place nor does he converse. During the 3rd week, the mourner sits in his normal seat. During the 4th week, the mourner returns to ordinary interaction. Rabbi Yehudah disagrees with these, delaying them all 1 week: Moed Katan 23a
Keeping the 30 days, or not, for one's Rebbe: Moed Katan 25b
Counting part of the 30th day as its entirety: Moed Katan 19b
Shaving: Moed Katan 14b [See Shulchan Aruch 390:1 that asssumes this is discussing the 30 day period as well as the 7 day period], 19b, 27b
Shaving during the 30 day period, following a holiday-interruption, if he didn't get a chance before the holiday: Moed Katan 19a-b
Laundering/Pressing old, new, or white garments: Moed Katan 23a, 27b
Allowing shaving on the Intermediate Days of Holidays if his 7th/8th is Shabbat, the day before a Holiday: Moed Katan 17b, 19b
Marriage during the 30 days, where he does [not] have sons, and is mourning a general relative: Moed Katan 21b, 23a
Marriage during the first 2 or 3 holidays after the loss of his wife, where he does [not] have children: Moed Katan 23a
Marrying immediately, to get support for his children: Moed Katan 23a
Greeting others and responding to greetings: Moed Katan 21b