Let's not forget the great Taiwanese eateries in Irvine's "Chinatown" at the corner of Walnut and Jeffrey, including my personal favorite, the Red Onion Cafe.
Mmmm... Tastes like pork!
Honda-Ya in Tustin or Shinsengumi Robatayaki/Ramen in Fountain Valley for Japanese.
Sagan (or any of 100 other Korean places) in Buena Park, or Irvine Tofu House in Irvine.
Banh Mi Che Cali, Quan Hy, Brodard (or any of 500 other Viet places) in Westminster and Garden Grove.
There's a whole section of "Little Palestine" in Anaheim, mostly on Euclid.
Plenty of great Mexican joints in Santa Ana.
Merhaba Eritrean/Ethiopian Restaurant on Ball and Dale in Anaheim.
Felix Continental (Cuban) in the Orange Circle receives mixed reviews on this board.
Vietnamese sandwiches at Mr Lee's are very yummy and really cheap. They have various locations in Orange County, but I usually go to the one on Brookhurst and Westminster. They are open 24 hours. Usually from 11PM-5AM, you can order through a little window, and each sandwich cost 25 cents more.
Well, Little Saigon in Westminster/Garden Grove, is a good place to start.
There are too many places to count, Brodard for great rolls, Banh Mi Che Cali for Vietnamese sandwiches, Com Tam Thuan Kieu for humongous rice dishes!