Two come to mind.
The first was my first 'big' brook trout. It was heavy and 21" long. There were other big fish around, bass and salmon. So, when I saw what it was, I got pretty excited.
The other was this year. I was meeting a guy I knew casually for some striper fishing. I overestimated the drive to our meeting place and got there early. It was a flat beach and the tide was low. It was also dark, about 90 minutes before sunrise. He wasn't around yet.
So, I walked across the beach and started out into the surf, playing out line with casts in front of me as I went. Something big, probably a striper, grabbed my fly and took off. I couldn't really see anything, which made the whole thing feel strange to me. I started walking backward through the surf pulling the fish with me until the hook came out. I felt the adrenaline for quite a while afterward.