The huge giant explosion- in Aliens (1986)
Simple works. That seems to be the mantra for many of the effect shots that impress me, including this one from Aliens. In the climactic escape from LV-426 our heroes barely outrun a gigantic explosion when the atmosphere processing station goes nuclear.
Once again, Bob and Dennis Skotak provided this shot for James Cameron, though I believe Brian Johnson shot the spaceship element - he shot most of the spaceship shots in the movie, favoring a frontlit/backlit traveling mattes approach, rather than bluescreen (that's a story for a different day).
The real trick here, however, is the mushroom cloud. It was done with fiber fill and a light bulb. I'm going to say that again: It was done with fiber fill and a light bulb! That's it! The fiber fill was used to create both the cloud cover, and the mushroom cloud itself.
A light bulb was placed in the middle of a mushroom shape, made of fiber fill. This was pushed up and the bulb was turned on in a carefully timed sequence. The drop-ship was added later. Completing the trick was the fact that the bulb got so hot that the fiber fill started to discolor, giving it that brownish look that resembles fire.
This is low tech filmmaking at its finest, but no less magical than a $1 million shot.