DH and I are expecting #3 in February.
Welcoming a bonus baby #3 February 2011!
I like Zoe with Abby and Kiera. I think it's a perfect fit between the two name styles.
I like Violet best from your short list. I like it best in general, because it's just sweet, feminine, grows up well, & it's not over done. I also like it best because it sort of bridges the gap between the classic Abby & the slightly more exotic Keira. Sophie & Zoe are cute too, but actually way more popular then Violet as far as I can tell.
Hope this helps!