A lunare wrasse will get way to large (10") and aggressive for a 90g. I had a 7" lunare wrasse in my 230g fowlr tank and he was aggressive.
http://www.liveaquaria.com/product/p...346&pcatid=346
I think the blue tang you're thinking of is also referred to as a hippo tang or regal tang. They get up a foot (12") in size, minimum of 180g.
http://www.liveaquaria.com/product/p...330&pcatid=330
A 90g is a bit small for tangs but if you really want a tang, a kole tang would be ok.
http://www.liveaquaria.com/product/p...345&pcatid=345