When I was thinking of middles for Sybil, Henrietta was one of my first thoughts, and I was crushing on Ivy at the time too, so Sybil Henrietta Ivy became my Sybil combo almost immediately. I still love it, but it's so rare a name will come together so quickly. I feel like Sybil goes well with some longer, Ancient Greek/Roman sounding names (if that makes sense) as well as longer, strong, feisty vintage names.
Sybil Octavia
Sybil Aurelia
Sybil Alexandra/Alexandria
Sybil Horatia
Sybil Georgiana (as George-ee-ah-nuh)
Sybil Beatrix/Beatrice
Sybil Helena
Sybil Francesca
Sybil Isadora
Sybil Thomasina
Sybil Nicoletta
Sybil Theodora
Fangirl (18) Dreaming of...
✦ Pandora ✦ Evanthe ✦ Marigold ✦ Beatrix ✦ Demelza ✦ Fae ✦ Sally ✦ Lavender ✦ Sybil ✦ Anna ✦
✧ Caspian ✧ Phoenix ✧ Ptolemy ✧ Horatio ✧ Nikolai ✧ Artemus ✧ Indigo ✧ August ✧ Lorenzo ✧ Prosper ✧
http://www.behindthename.com/pnl/1396