I love all the [name]Belle[/name] names! [name]Annabelle[/name], [name]Clarabelle[/name], [name]Mirabelle[/name]… [name]Do[/name] you know of any others? Also, would shorter, simpler middle names work best?? Thanks in advance!
[name]Cybele[/name] is almost a belle name!
[name]Maybelle[/name]
[name]Amabel[/name] has the sound
[name]Arabelle[/name]
[name]Corabelle[/name]
[name]Ishbel[/name] (his is a favourite of mine!)
[name]Maribelle[/name]
[name]Adabelle[/name]
[name]Bluebell[/name]
[name]Abelle[/name]
[name]Marabelle[/name]
[name]Melibelle[/name]
[name]Orabelle[/name]
[name]Rosabelle[/name]
[name]Anabelle[/name]
[name]Willabelle[/name]
The only other I can think of is [name]Arabella[/name].
I love them, too. 
Some middles:
[name]Annabelle[/name] [name]Hope[/name]
[name]Annabelle[/name] [name]Jane[/name]
[name]Annabelle[/name] [name]June[/name]
[name]Annabelle[/name] [name]Kate[/name]
[name]Annabelle[/name] [name]Mae[/name]
[name]Annabelle[/name] [name]Maeve[/name]
[name]Annabelle[/name] [name]Scarlett[/name]
[name]Annabelle[/name] [name]Violet[/name]
Good luck!
[name]Carabelle[/name]
[name]Christabelle[/name]
[name]Clarabelle[/name]
[name]Idabelle[/name]
[name]Jezebel[/name]
[name]Mabel[/name]
The one I’d add is Lilybelle, which I think is cute. I do think that shorter middle names would work best.
Somehow [name]Isabelle[/name] was forgotten–thought I’d toss her into the mix
I like [name]Mirabelle[/name] since its not as common. [name]Mira[/name] could be a cute nickname.
I like a 2 syllable with [name]Mirabelle[/name].
[name]Mirabelle[/name] [name]Anais[/name] (I like the flow and the french continuity)
(This is a bit off topic, but related, so I thought you might find it interesting.)
We recently had our second girl and named her Aila (“Eye-la”). We were searching for a nn for her soon after she was born and “Ailabelle” came out of my mouth and has stuck (she’s about 4 months now). We call her Ailabelle and babybelle so much that our two year old daughter thinks her sister’s name is “Ailabelle”!