After trying literally hundreds of different IPA's (I used to keep track), I have to say Stone Enjoy by... is my current #1. Also I went to Columbus Ohio again this spring and had plenty of Columbus Brewing Columbus IPA. Still ranks up there for me. Another new favorite of mine is Blackrock 51k ipa. So I'll go with those 3 for now:
Stone Enjoy By (this seems to be on most lists, for obvious reasons)
Lagunitas Hop Stoopid
Stone IPA (2 stones, yea but this is year round and a staple in my fridge before I had so much home brew always on hand)
Lagunitas Sucks (like many other folks, this is my hands down #1)
DFH 90 minute
Stone Go-To, which I find to be impressively hoppy for a low-ABV beer.
I should mention that, being a midwesterner who has never participated in a long distance trade or made a beer pilgrimage to either coast, I haven't had the opportunity to try such mainstays as Heady Topper or Pliny the Elder/Younger.