Synonyms for Dumbfounded (same or very similar meaning)
WordNet sense 1 (as if struck dumb with astonishment and surprise):
dumbstruck, flabbergasted, stupefied, thunderstruck, dumfounded, dumbstrickenWordNet sense 2 (taken unawares or suddenly and feeling wonder or astonishment):
surprisedFrom the ODE community, based on WordNetadd/edit