The best reference tracks ever are all the songs you've ever heard that brought you closer to music than ever before! Seriously, if you need "a list" of reference tracks to reference, I'd argue that you're probably in the wrong hobby/business. We've all heard great & amazingly well produced songs before, regardless of genre that we respectively like. And guaranteed that we all know (and will never forget) what songs those are. So hell with a list. Use you're musical compass: you know exactly what to "reference" already.