Good answer, Jeff! (o sea "Vaya, buena respuesta!) In general, I'd translate "vaya" as "wow." You could also use "Man" or "Boy," Note that in this context, we usually say "man" or "boy" even when talking to a girl, for some strange reason.

I have not heard theses expressions before. Here it say "vaya cara" is "what nerve". http://www.wordreference.com/es/en/translation.asp?spen=%C2%A1vaya+cara! So the first one would be "What nerve! What's wrong (up) with you! The second "What nerve! What's bugging you today?" You could also say "Wow, who peed in your fruit loops this morning"