Oh, I just remembered another...
They are twins, and their names are Destiny and Trinity. They are my age and are total opposites. Destiny is a happy-go-lucky, artsy, book-reading optimist, and Trinity is a dark, Shakespeare-loving, technofreak pessimist.
Also, there's one I call Sabrina, who is a little tiny 4-year-old that I take care of because her parents were murdered. She's really hard to make friends with, because she saw the whole thing and the trauma almost made her go crazy. I'm the only one who can talk to or understand her.
How I love Imaginary Friends!