I found a neat Wikipedia page with a lot of old C64 box art, so I figured I’d post my favorites over here. I tried to find a variety of different styles. Sorry for the low resolution, I’m not sure where to find better versions.

Advanced Dungeons & Dragons Dragon Strike, a painting of a man riding a dragon chasing another dragon through the sky and breathing fire at it

Cutthroats, a scuba diver is looking up into the camera with a scared expression. He's holding his cut airhose in his hand.

Battletech: The Crescent Hawk's Inception, some soldiers are hunkered behind the legs of a giant robot and shooting another giant robot with lasers. The attacking robot had a ball turret underneath the middle section and two chicken-like legs sticking out of the sides. Behind that robot are more soldiers attacking with it.

The Great Escape: A pair of hands are in the fore, gripping the barbed wire crossing the scene as if climbing. Behind are a couple of men running for the barbed wire and away from some structures and searchlights.

Maniac Mansion: In the foreground, 5 teens: a cool cat all in black, a sporty guy in a denim jacket and jeans, a geek shining a flashlight at his face from underneath, a chic-punk girl with big hair, and a barefoot blonde surfer dude with a board. Behind them is a landscape with a creepy mansion, a meteor flashing overhead. There is a faint outline of a man giving a sinister smile in the sky.

If there’s interest I’ll post more, and from other systems.