Remember that a lot of these places have regional fare much like the U.S.
Mexico has several different regions, some with the more Tex-Mex flavor and others (coastal) that are more focused on seafood.
Italy has similar divisions, as other have noted, so does Germany.
Japanese is one I assume you have tried, but has different regions you may want to investigate. Indian food again has several regions with their own cuisine.
Not sure on the regional differences of Vietnamese food, but there is a lot there. (Their Bánh mì sandwiches are an interesting result of french colonialism.)
Thai is another common "exotic". Love the curry.
Korean is another that is very good. (Try the barbecue)