Good topic! I usually tend to favour more detailed album covers, so it was actually a little difficult for me to find examples that fit, but I ended up coming up with a few that work if you don't mind a bit of writing on them.
Alas - S/T - Not what I'd necessarily call a "great" album, as per your original post, but it's a pretty decent ELP-like Argentinian release.
Arco Iris - Agitor Lucens V - Okay, this one I'd definitely consider a great album. And I think the cover still somewhat fits what you're describing.
Arco Iris - Arco Iris - More of a straightforward folk rock album than
Agitor (if I remember correctly), but the cover is definitely minimalist enough to fit here.
Magma - MDK
Nucleus - Elastic Rock
Some of the covers from the Grateful Dead's
Europe '72 series also use the same sort of design.
And let's not forget about the most famous example of all time!