Firstly, I'm a longtime lurker on Chowhound, but a first time poster.
My wife and I just returned from our first trip to Oaxaca, and had so many wonderful meals it's hard to remember them all. That said, there are a few that stand out.
First and foremost is El Naranjo.
Prior to our trip down, my wife did some research and heard about this restaurant - but, we had also heard that it had closed. However, on our second day, we ran into a gringo named Andrew Peterson who was passing out flyers to his restaurant - as it turns out, he bought El Naranjo from the previous owner. Well, we were a little skeptical, but decided to try it anyway - boy are we glad we did.
For an appetizer I had a camarones cocktail that was out of this world. My wife had the flor de clabaza con queso (squash blossoms with cheese). For the main, we both had the Mole Negro which was superb. The atmosphere was relaxing, the wait staff super attentive, and the prices very reasonable. It's right off the corner of the Zocalo.
As an extra added bonus, we got to know Andrew and his wife a bit - they gave us all kinds of other great recommendations, including a restaurant on the way to Mitla. (If you're ever 3K away from Mitla, look for the sign that reads "Donaje.") We spent 2 hours there, talking with her, watching her cook, and then eating her amazing Mole and home made tortillas.
Anyway, I've read a few postings about how El Naranjo was closed, and wanted to give my 2 cents about the new management.