Pyunkang Yul Essence Toner (200ml for $14 on eBay, 100 ml also available)
I don't classify this product as an essence -- it is a pure toner in my eyes. But oh boy it's good. It's super hydrating and layers well, and although Laneige Cream Skin Refiner is still my nr 1, this one is definitely very high up. What I also love is that the inci list is relatively simple. A simple product that works well! .