Indian buffet in OC
The Indian Cook House's buffet in Irvine (off Culver) is actually one of the better buffets I've seen for Indian food. It's a little bit americanized (not very spicy) but still very good and for 5 bucks for an all you can eat lunch buffet you can't go wrong. They have a decent selection which even has desserts. The carrot stuff they have for desert (I forget the name) is awesome. Make sure you go before noon unless you want to wait for a table. The one drawback is that the place isn't very big.
I'd also like to recommend Laxmi Sweets and Spices off Newport in Tustin. It's an Indian grocery store that also offers an all-you-can-eat lunch buffet for about 6.40 after tax. Naan comes with the food, and it's pretty great. Though I only eat the vegetarian dishes, it's a lot of good Indian food for cheap.