In no particular order [and probably with some omissions]
1. Lal & Data
3. Spock dying
4. Spock's funeral
5. The Inner Light
6. The breakdown in, 'Far Beyond the Stars'.
7. Neelix leaving at the end of Voyager.
8. Tasha's funeral.
9. T'Pol and Trip dealing with the death of Elizabeth.
10. B'elanna and Tom revealing their feelings for each other while drifting in space.
11. B'elanna revealing why she wanted to change the looks of her child.
Im sure I will think of more...