My only viable option if I'll be taking off my jacket is a Taurus 738 on my weak side interior ankle. It's the only thing I have small and light enough for ankle carry without discomfort. But such a gun is strictly utilitarian and hardly seems appropriate for black tie.
If I knew for sure that my jacket would not be coming off, which is the case most often for a suit and almost invariably for a tuxedo, the options open up to anything I can carry in an IWB rig or a higher-riding belt rig. I'd carry something with more capacity or at least in a larger caliber. And since it's black tie, carrying a plastic gun would be just wrong, so it'd be either a Baby Eagle, a BDA, or a revolver.
I'd have to pick up a black holster for my 2.5" Security Six. Yeah, I think that'd be my choice.