RH Potter does lovely work. It's semi-abstract with a calligraphy brush feel.
This one has some fire sparks that could be expanded into really cool butterflies:
http://www.rhpotter.com/tattoos/fire.html

I commissioned this one from her and have it on my upper back:
http://www.rhpotter.com/tattoos/phoenix3.html

And, hey, I found a butterfly in her archive section. :)
http://www.rhpotter.com/tattoos/butterfly.html