THIS IS JUST MY OPINION.

11. Martha leaves the Doctor - Last Of The Time Lords
10. Rose is left on the beach (again) - Journey's End
9. Amy's death - The Angels Take Manhattan
8. 'I am not a Dalek!' - Asylum Of The Daleks
7. Amy and Rory fall - The Angels Take Manhattan
6. Donna realises what's happening to her - Journey's End
5. Donna doesn't remember the Doctor - Journey's End
4. The Master "dies" - Last Of The Time Lords
3. The Tenth Doctor's breakdown - The End Of Time Part Two
2. River's message - The Wedding Of River Song
1. Reinette's letter - The Girl In The Fireplace