Heard talk of this list on the board and ran through it. Just a chowpup here, but a few comments to stir up discussion:
For Peruvian, Cuzco on Columbia Pike is a glaring ommission. I haven't been there within the last year, have gone a number of times in years past, and their lomo saltado is excellent--way better than Costa Verde's which is merely average. It always has Andean clientele and this group is not a large one in the area.
For Salvadoran, Restaurante Abi also on Columbia Pike. This place was here 15 years ago prior to the proliferation and I can't comment on the food as I haven't been there in at least 5 years, but should be listed, unless it is closed. It is to Salvadoran places what Food Factory is to the kebob.
I was pleased to see Pilar's on the Salvadoran list, it is amongst the better Salvadoran places with the best pupusas I have had in the area, though note I have not ventured into Arlandria. Most everything there is done a little better than most of these types of places (the Enchilada Guatemalteca is a must if you go). Note that they used to be in their own building on Telegraph, but within the last month relocated to a dangerous looking strip mall (w/ the 7-11) on Huntington Ave. The ambiance is horrible now--even for a Salvadoran place--but the food is still a notch better than the competetiors. Expect the typical surly service--don't be offended, they also treat their own that way.
I have to disagree that Old Town is in general mediocre--the author is clearly prejudiced in this regard. Though other areas of the metro--which the author is certainly more familiar with than Alexandria and points south--have great offerings (wish I was motivated enough to make the trek), Old Town offers so many choices of varying quality that a general statement like that is just plain not accurate.
Awesome list, though, I plan on making my way through it.