I had a friend named Isadora in grade school and she went by Isa. I thought it was gorgeous. I wonder how many of the gazillions of Isabelles as going to go by Belle and how many will discover Isa.
The first thing I thought of was Isadora, which a couple other posters have already mentioned. Here are some more that don't necessarily have a similar sound but do have a similar feel IMO:
Imogen
Angeline
Eloise
Genevieve
Juliet (or Juliette, but I personally prefer the other spelling)
Re: Name alternatives
Heavens to Murgatroyd Blog
Unofficial Baby Names Sticky Note: New and Old| Local Bumpie Website
Annabelle
That's all I've got.
He's my fairytale, a dream when I'm not sleeping.
<a href="http://s279.photobucket.com/albums/kk121/behapybride/?action=viewIsobel
Sable (love)
Sabella
Sybil
Isa
The first thing I thought of was Isadora, which a couple other posters have already mentioned. Here are some more that don't necessarily have a similar sound but do have a similar feel IMO:
Imogen
Angeline
Eloise
Genevieve
Juliet (or Juliette, but I personally prefer the other spelling)
Adelaide
Estella
Rosaline