Japanese: Have been delighted by Nagomi, on Plymouth in the space where Bagel Fragel used to be (it is still there but has moved several spaces down). Only downside: as in heaven, there is no beer. But the sushi dishes are all very elegantly presented, even the basic specials. Homemade soy sauce that isn't too salty and really tastes like soy. Simple, hearty noodle dishes are about $6.50 or $7.50; you can pay a lot more than that for noodles in this town.
Mexican: There are places like Pacific Beach Burrito (on Washtenaw, between Golfside and Hewitt) on every block in SoCal, but around here it's unique. Very cheap (tortas: $3.99 or $4.25, which is less than in Detroit), tasty Mexican standards. This place is catching on, and they're understaffed, so the fast food aspect isn't so fast if you go at peak hours. However, they hang in there, and eventually you get the food.