Male leads are single fathers:
Oh! My Lady - Main plot element. The male lead is a famous actor and finds himself with a daughter he didn't know existed. Female lead helps him come to terms with it (you guess the outcome). Not an outstanding drama, but it fits what you're looking for, romance takes the back seat and the male lead growing up is the key point.
Ms. Temper & Nam Jung Gi - A good side part of the story, the male lead's son is really great on his own and his scenes with the female lead are the best. I highly recommend this one, hang on through the first episode, it can be a bit disconcerting...
City Hall - really just a side element, but there are a few cute scenes.
For single mothers, I'll second Panda,
Please come back, Mister is very good, not quite as straight forward in the "single mother" part, but one the female main is divorced (the father is another male main - the bad guy), and I guess you can count another female main as a widow raising her daughter (even if the main male lead is actually the father but no one knows it). I'm pretty sure my explanations aren't making sense but the drama is difficult to sum up, complex, but really good.
