I'm hoping this will be a fun conversation starter. Actually, I'm just hoping no one's confused by the question.
To expand, I'm asking for restaurants that you've stumbled upon yourself, without the help of Chowhound or Yelp (or what have you), that you really enjoyed, and then only later did you realize, ether through trying other similar restaurants or from reading reviews, that what you were having was the exemplar of the food in question.
For me, it's ramen at Santouka. I grew up eating instant noodles, and didn't have much experience with real ramen and ramen houses. When I moved to L.A., I "discovered" Santouka and have been eating there for years (it's convenient to where I live), and never really had any desire to go anywhere else, but I only recently found out that it's considered one of the best ramen places in L.A..