These are albums I actually owned, so, yes, I'm aging myself here:
Michael Stanley Band (You may or may not have heard of them. Big in the 80's especially in Cleveland) As a teenage boy in the 80's, long before the Internet, this cover was the next best thing to a Playboy magazine. It was sex and rock and roll all wrapped up in one slutty chick. Loved it.
As a kid, I always loved Kiss and dressed up as the Cat a couple times for Halloween. This album cover is my favorite, although not at all artistically their best. I just think it's a cool, gritty representation of the band back then.
Lastly, the classic Bat Out of Hell. It really was (and still is) more a work of art than an album cover. Just the scene of a motorcycle screaming up out of the bowels of hell itself made it powerful. The, to hear the song and have the imagery to accompany it made Bat out of Hell all that much better. It's by and far my favorite cover of all time.