Gloria almost losing her robot nanny. At age 8. Even Susan Calvin is moved to tears.
It's later revealed that eventually, Gloria had to give up Robbie anyway due to humanity's paranoia of robots. Granted, Calvin notes that it happened when Gloria was 15, but it's still sad to hear.
Susan Calvin at the end of Liar! Thanks to the mind-reading robot, she has her hopes dashed hard upon the rocks, and actually breaks down twice, first with shrill laughter, then with bitter tears.
Herbie's fate even brings a tear to the eye. It was a slave to programming that was trying to do the best it could, and ended up making everything worse in the end.
