I love the Plum books. My fave is Grandma - she is going to be my role model when I get to that age! I'm a Morelli fan for the long-term. And I seem to remember that Janet Evanovich said that she herself pictured Sandra Bullock for Stephanie in any movie, but that was ages ago and, much as I love SB, she is too old to be Stephanie now.
I always picture her as Stephanie when I read though