Aight, it's time I give back to you folks who have helped immensely in my questing for all things delicious.
I've explored the Yucatan over the last few months, and have found a number of places I'll share, as well as a few I wished I'd managed to avoid. What follows is something of a mini-dissertation:
For classic "Mexican" comfort food, do not miss Platos Rotos in Centro at 33D and 72. It's surrounded by the slow food market every Saturday, of which you'll likely hear. Platos Rotos is run by chilangos (folks from Mexico City) and is a popular lunch spot full of regulars; the menu is written on a chalkboard (but not in the pretentious way). You'll be served beans (sublime) and salsa (wonderful). The mole verde is one of the best I've ever had. Menu changes daily; vegetarian options abound (rare). I highly recommend a coffee, unusual in that they prepare it in an older style that is now fairly hard to find. Don't be afraid to ask to try (probar) one or two items before ordering. Show enthusiasm for the food and you'll be showered with offerings. Lunch here is reasonable and wonderful. I go three times a week at least.
For more "classic" (highland-style) Mexican, Ana Sabrina's tacos are fairly famous. She's from Mexico City, and cooks the best mole I've ever had. My father said it's the best he's had since the 70s (he studies Mexico and has lived and traveled across the country). You can find her Saturday nights at Noches de Merida (odd little karaoke sing along) at the bottom end of the Paseo Montejo and Sunday mornings in Parque Santa Lucia at the Viejoteca (bring your dancing shoes). You MUST order the mole and the papas con chorizo. Her tortillas are the best in town. She's absolutely lovely and sweet and has a brilliant smile; she's also an astute business woman.
Apoala in Parque Santa Lucia. This is Merida's Oaxacan restaurant. Avoid lunch as it's hit or miss. Dinner on Saturday/Sunday night is best. It's good but pricey, and you can find similar restaurants in Mexico DF and most major metropolitan cities. Pricey. Highly recommend the salads. Atmosphere is excellent and the service is top notch, but the food just isn't remarkable and its all very predictable.
For Yucatecan cusine you have several options. In the mornings you'll find relleno negro (which has never impressed me, and I've had it everywhere), poc chuc (same), relleno blanco, etc., in the stalls inside Parque Santiago. The real star of Parque Santiago is La Reina Itzalana, open every night after 8. Go Sunday as everything is best on Sunday. This is the place to try panuchos (if you don't make it to Valladolid), salbutes, and all the little things you've heard/read about. Be sure to order the queso napolitano--the regional flan. It's fantastic. Lots of color here.
For Yucatecan food try the restaurant inside the department store Chapur (Norte, Circuito Colonias/Calle 26 in Itzimna north of Centro). Every day a different Yucatecan dish is on speciality. It is inside a department store, which is strange, but whoever is in the kitchen knows what they're about. Yucatecan food is lunch only.
For non-Mexican, do try Oliva (Italian, homemade pasta, excellent), Cafe Creme on 41 near Paseo Montejo (French, croissants, spinach quiche, desserts), Lebanese pastries to die for at a little place with irregular hours just North of the monument at the top of the "Centro" section of Paseo Montejo, Tacos Arabe (avoid the tacos!). Adjacent to Tacos Arabe (may have a different name, but you can't miss it if its open), there are a few men and a few pots and pans (nights only). They have tamales. Order a few salsa verde and salsa roja and experience transcendent bliss. Also go to Hidalguense on 56 in between 61/59 for incredible quesadillas. Try the huitlacoche (Mexican corn mushroom, OMFG) and more importantly be sure to get there early enough before they run out of flor de calabasa (absolutely entrancing). Excellent homemade salsas. I like to watch/endure Laura Pozzo or the telenovelas that shriek from the television; you may see me trying to read DH Lawrence despite the racket. There are at least one or two other Hidalguenses in Merida. They're all on horrible bus streets, but absolutely worth the trek.
Well meaning people will direct you to a taco "stand" in Itzimna called Wayane. They don't know what they're thinking! It just isn't good and its way out of the way of everything...there is, however, a great place to watch movies nearby (Cairo Cinema Cafe) also good is La 68 but don't eat there and especially avoid the coffee, they've tried to poison me twice with whatever it is they call latte.
For coffee you can purchase wonderful beans from Riqueza de Chiapas on 60. Bring these home. They're magical and wildly underpriced. Be sure to get a receipt so as to avoid customs hassles. This is some of the best coffee I've had outside of Colombia (Sierra Nevada de Santa Marta). Don't get the cheap stuff! You'll regret it, I promise. Ask to smell the beans. Maybe see if you can walk into the back and smell and look. Coffee heaven.
Martha Stewart's coconut drink place is on 59 between 66/64. They have fresh coconut water and it's very good and fairly priced.
If you're adventurous (and you should be), go to the bus station CAME and have the barbacoa at the Chiapas place on 70 between 69/71. They also have a soup. Both are very good, but the barbacoa is a thing of beauty.
Chaya Maya: avoid this like place like salmonella. Avoid most anyplace recommended by guidebooks or tripadvisor as schemes abound in Merida.
BEST COCHINITA PIBIL IN THE ENTIRE WORLD: El Gallo at 41/46 at the North end of the street that leads to the Convent. Run by a wonderful elderly couple, this is absolutely some of the best pork you'll ever eat, I think.
For the best panuchos on the Peninsula (arguable), try Selva way up on 42/31.
I also like Conado in Valladolid, more for the atmosphere. There are a few fancy places in the city. These I've avoided; I doubt they're worth the trip. Bottom line: if you're in Valladolid, do not miss cochinita at El Gallo--like Bogie said, this is the stuff dreams are made of.
Avoid Kinich. It's NOT good and its outrageously overpriced. I do not understand the rave reviews and find them suspicious. I've eaten here multiple times/days/meals. It is perenially disappointing, especially after Valladolid. Izamal cannot compete with Valladolid, in any way, really.
Finally (I hope this isn't too overwhelming, but its my first post and I've used this site so I felt obliged to give back):
PLAYA DEL CARMEN/TULUM
Today I ate all the tacos on offer at La Floresta in Playa del Carmen. Camaron and Pescado were far and away the best, as was the green salsa. It's on the other side of 307 on 14.
Do try the Chocolate Tradicional at one of the Ah Cacao locations on 5th Ave. This is traditional-style Mexican Chocolate, which has become very difficult to find. It's well-made at Ah Cacao (I've had it every day on this trip to Playa). The dark chocolate bars are aslo very good; the elote cake (corn cheesecake) is strange but not necessarily bad. It's different!
Do not miss the tacos el pastor at Antojitos la Chiapaneca in Tulum pueblo. Off the main road, westside. This place has been discovered but it's really good.
Whew. I hope this proves useful and delicious. Enjoy the Yucatan and enjoy Mexico, one of the best places to eat in the world. I may post another list but this is a good start.