I love, love, love the name Olivia! :-) It's one of my top favorites for a girl. I find it to be such a classy, feminine-sounding name, and the nickname possibilities are great imo. My personal favorite combo is Olivia Rachel, but here are some other suggestions:
Olivia Celeste
Olivia Christine
Olivia Carys
Olivia Camille
Olivia Charlotte
Olivia Caroline
Olivia Faith
Olivia Felice
Olivia Grace
Olivia Gabrielle
Olivia Genevieve
Olivia Guinevere
Olivia Hope
Olivia Iris
Olivia Isabelle
Olivia Josephine
Olivia Jasmine
Olivia Josette
Olivia Jaclyn
Olivia Kathryn
Olivia Kate
Olivia Michelle
Olivia Marie
Olivia Martine
Olivia Nicole
Olivia Payton
Olivia Paisley
Olivia Presley
Olivia Rose
Olivia Raine
Olivia Reese
Olivia Selene
Olivia Sadie
Olivia Therese
Olivia Taylor