So not to be the total opposite to the other thread, since I think it will be quite limiting to find stuff with great cover art and bad music. Let's focus here on great cover art, irrespective of how the quality of the music is. Although we can of course discuss the music as well.
My first example is this one, and depending on who you ask the music might be great or bad or something in-between.
https://www.discogs.com/SFX-The-Unreleased-Tracks-89-94/release/68966
I never liked any of the tracks on it, as they did sound dated even when it was released. Perhaps it's interesting to hear how their sound developed since then. The artwork on it is an entirely different thing. It looks amazing even to this day with its handdrawn very psychedelic artwork. Funny thing is I didn't even notice that it has the letters SFX camouflaged into the organic looking mess, until just recently. Which basically makes it organic acid graffiti. A friend of a friend had this one as an original poster framed on the wall. Really nice
This one is OK, not mindblowing but also benefitting from the organic handmade quality. Perhaps the slightly anime-influenced style makes it a tad bit on the cheesy side of things. Since I think there has been a lot of anime inspired stuff in full-on etc. So that is definitely overplayed.
https://www.discogs.com/Various-Lunar-Civilization/release/83307
This CD though, has a real banger: Wizzy Noise-Shores Of Freedom
Epic track still!