In Sander Cohen's apartment, you can find a male and female Splicer slow-dancing together. No violence, no spewing hatred. Just the two of them, deeply in love, enjoying each others company. They won't even attack you unless you disturb them. For the romantic player, it's oddly touching to see that, even in the depths of depravity that Rapture has become, love can still exist.
The Good Ending: Jack returns to the surface and raises five of the Little Sisters as his own. Each of them live full, enriched lives, and are at Jack's deathbed, each clutching his hand.
That ending moves this troper to tears every time.