My favorite series is the Little House series by Laura Ingalls Wilder. I've already mentioned that series, so I think I'd have to go with Elizabeth Berg's three books (Durable Goods, Joy School and True to Form) featuring recurring character Katie Nash.
Durable Goods is a story about a twelve year old Army brat, who has recently lost her mother to cancer, coming to terms with an abusive father. Katie lives on an Army base in Texas with her father and her older sister, Diane. When Diane escapes their home in the middle of the night with her boyfriend, Dickie Mac, Katie goes along.
Joy School is a story of first love. Kate is thirteen, and the object of her desire is a 23-year old gas station attendant named Jimmy. He is married and has a child, but as Katie says (after noting that he does not wear a wedding ring) it's every woman for herself. 
In True to Form, Katie has moved from Texas to Missouri, and is having a hard time finding friends. She longs to be in with the in crowd; instead she and her one friend are classic losers. The story is about how hard it can be to admit yourself to yourself, to live your life in a way that is congruent with what you really believe.
