Little naff, but our honeymoon was one of my favourite holidays. Best night was staying a night in a cheap Best Western in Key Largo and finding out there was only one place we could eat that didn't involve getting back in the car.
It was a little tiki bar just along the road and we walked down there and had one of the best nights out I've ever had. Ice cold beers, great seafood, some locals jamming and playing live music (think Jack Johnson type stuff) and I helped lift a rescued turtle off a boat so it could be transferred to the turtle hospital down at Marathon. It was huge and took 6 guys to lift it.
We went back a few years later hoping to relive the experience, but the bar had either been knocked down, been blown down by a hurricane or had burnt down because all we could find were some remains about a foot high.
Have had some other great days on hols, though. Helicopter ride over the Great Barrier Reef, horse riding in Yellowstone Park, killer whale watching off Vancouver Island in a boat smaller than some of the orcas swimming around us, hiking in the Virgin Islands...