there's quite a few to choose from, but one that works on so many levels that others just don't approach, a 10 in my book, is "tap tap" @ 819 fifth st just west of collins. haitian food that is wonderfully spiced and ridiculously cheap. owned by a documentary filmmaker, it's got a sense of style you just will not see anywhere else.
pumpkin soup w/cabbage, spinach in curry sauce, grilled conch w/garlic sauce, any of the whole fish of the day w/lime sauce, grilled goat tidbits w/watercress dipping sauce, malanga fritters, the definitive mojito made w/5 star 8 yr old barbancourt rhum, considered one of the best rhums of the world (you need to specify w/rhum). save room for the banana fritters for dessert.
a visually stunning set of rooms (i prefer the back room) that are like entering a haitian style pix. all walls, chairs, tables, are painted as such. the bathrooms are a must as is the art gallery upstairs. if closed, you can usually persuade them to open it for you.
in addition to all of this, on thurs and sat pm, the ex mayor of port au prince, manno charlamagne (who has a voice from the gods) holds forth w/a small band. acoustic guitar, sax, bass, some percussion, think of a more rhythmic gypsy kings but w/soul. you can not go wrong.
after living there for nearly 10 years i found it to be a rich culture and cuisine well worth exploring. you will be a hero w/this one. everyone i've ever taken there is blown away, often becoming the highlight of the trip. nothing like it anywhere else, and isn't that why we do this in the first place?
"In pursuit of joys untasted"
from Giuseppe Verdi's La Traviata