What's the first lens that made you say "Wow"

Although my 50 1.8 was my first prime, and when I pulled up the shots I took with it on my pc I was like, "sweeet! This lens is so cool!", my first wow moment was when I got my 300 f/4 last week. I hadn't even mounted it on the camera yet, but when I opened the case, pulled it out and held it in my hands for the first time, I literally said "Woooooow". Now I see what the fuss is about with the big white lenses. This is a serious piece of gear.