I love anything that comes from the Yirgacheffe or Guji Regions of Ethiopia. The first time I had a single origin from Yirgacheffe and tasted blueberries my mind was blown. Didn't know coffee was "supposed" to taste that way. I've had similar experiences with coffees from Kenya, Burundi, and Rwanda. Any coffee that gives fruit notes is an instant winner for me.
I know this sounds pretentious but I had a $20 espresso of Geisha grown in Panama that I don't know will ever be topped. Still can't believe the clarity of that coffee.