I've been almost overwhelmed with all of the blue options since posting this thread, but I thank you all nonetheless!
So many come with other issues such as dietary needs or possible aggression toward similar species that I need to spend some time studying them all.
There are too many to choose...
I would definitley say that springeri damselfish are one of the most peaceful damselfish, I have one with a firefish and the firefish stays untouched. They may bicker in groups but they also look awesome in groups.
I still say a yellowtail blue or springeri damselfish is your best bet. Incredibly bright blue, shouldn't cause any trouble due to being added last, stays small, will eat whatever you feed it.