Jemima

I have a Jonah and a Norah.

Jonah and Madeleine

Jonah and Frances

Jonah and Lily

Jonah and Ruby

Jonah and Penelope

Jonah and Olivia

You have lots of good Biblical options: Leah, Sarah, Rebecca, Ruth, Naomi...

I immediately thought of Elizabeth. I don't think it's overused, especially if you go by the full name, instead of a nickname.

Just don't do Johanna

Elsa

Rebecca
Sarah
Emily
Abigail
Elizabeth
Rachel
Naomi
Hannah

Kate

I love Jonah, and think you've got lots of great suggestions here.

I generally like sibling names to match in terms of popularity and ethnicity, so I'd probably choose another biblical name that isn't either unheard of or very common.

For example:

Susannah
Lydia
Eve or Eva
Naomi
Esther
Miriam

to go with a name that ends in a "-nah" sound, I prefer something that ends differently, like

Claire
Elizabeth
Laurel
Lauren
Eve

Lila

Clara
Susannah
Cora
Leah
Cecilia

I think Baby Name Wizard is pretty good at sibling suggestions: http://www.babynamewizard.com/baby-name/boy/jonah. From this list, I like Lydia a lot. You could also try Susanna, or any of its related spellings, which is also from the Old Testament...I also think Helen, Vera and Willa are nice classic names.

We're having a tough time coming up with girl names. Any thoughts? As you may guess from my son's name, Jonah, I like names that are classic and fairly simple but not overused.