lots of them, lately.
Into the Mystic (best song ever) by Van Morrison, because it was "our song" with recent ex.
To the Morning by Dan Fogelberg. Ex's parent's song, has a lot of emotional connection for one particular point in our relationship (when we were really falling in love).
Country Roads, by John Denver, bc ex used to sing it to me to help me fall asleep, especially when we were long distance.
Goodnight Elisabeth by Counting Crows, because it reminds me of another ex and another sad time.