Roberto's, San Diego
Back on the US side of the border, Roberto's (and its competitor Alberto's) is a late night post-drinking fave due to its greasiness. What's interesting is that this is a uniquely San Diego version of Mexican food, which is not really available elsewhere. The key is in the overloaded cheese on everything, as well as the heavy grease dripping out of taco shells and the like. Not the healthiest food in the world, but late night food seldom is.
At least they have horchata, which is a sweet Mexican cinnamon rice drink. Yum.