자기 - Dear/Myself
This one is a little hard to explain. It is usually translated as my dear but its more than that. It means more like 'you're a piece of me'
But calling someone "peice of me!" in English isn't quite as cute.
여보 - Darling, honey, sweetheart
This like all English pet names rolled into one. Sweetie, honey, darling, etc. However, its an older term so usually only married couples feel comfortable using it. It's sort of a sign that you are married and in this for the long haul.
내사랑 - My love
Literally, "my love."