Some of my favourites are:
1. AFI - "Black Sails In the Sunset"
I like it because it appears to look like a painting of sorts. I'm in college right now for graphic design / illustration, so I can really appreciate this kind of art. Plus, the album is awesome. I love all their covers/music. All of them have some kind of mystery or something literal that's relating to their music.
2. The Clash - "London Calling"
I'm not sure why I really like this cover, but it's one of those covers that you don't even have to see the band name anywhere and you just know it's The Clash.
3. Saetia - "A Retrospective"
This album cover is very simple like, The Beatles - "The White Album". I'm also a big fan of very simplistic and not overdone covers. Sometimes you don't want a big fancy cover and just something simplistic and not right in your face.
4. The Misfits - "Collection 2"
The cover is one of my favourite skull logos by The Misfits. I really enjoy all of their covers/logos though.
5. Jawbreaker - "Unfun"
Cats are my favourite kind of animal/pet, so this cover I just had to say it :)
*I have a TON of other favourite covers too, but that would take me all day and would be a very long post.