Here is a list of 10 more albums that either has less than 500 listeners on last.fm or is great but way under-listened. Also I'll link the best song on the album.
1) Emerson, Lake and Palmer - Black moon
---Affairs Of The Heart
2) Emerson, Lake and Palmer - In the Hot Seat - Though More relaxed than their earlier works these are two quality progressive rock albums.
---Hand of Truth (Preview from some site)
3) Bee Gees - High Civilization - Their best overall album other than Saturday Night Fever. It came out in 1991 when they were past their peak of popularity so almost no one has heard of it. It is some cool, unique 90s-style rock and everyone should check it out.
---Evolution (Amazon Preview)
4) Big Daddy Kane - Veteranz Day - His latest album. This is just a great hip-hop/rap album, if all rap was like this I would love it.
---Uncut, Pure (Amazon Preview)
5) Biz Markie - All Samples Cleared - His last album of the 90s due to the lawsuit. He sings like a drunk most of the album (maybe he is drunk?) and somehow it makes the album quite unique and enjoyable.
6) Black Sabbath - Dehumanizer - A concept album about computers taking over the world basically. It is Black Sabbath's best album. It's difficult to pick a best song since they are all so amazing. I'll pick
---TV Crimes since it has a power metal feel to it.
7) Slavior - Slavior - The best way I can describe it is "The Next Level of Rock." And I hope they quote me on that! :P
---Red Road (Radio)
8) Suicidal Tendencies - Freedumb - Robert Trujillo on Bass + Funk Rock = Great album. It's the only ST album that doesn't make my ears bleed. So I have no idea why the play counts are relatively low.
9) Angra - Fireworks - Angra's best album. The last one with Andre Matos on vocals. Yet it's their least listened album. What the hell? Go listen.
10) Naildown - Dreamcrusher - Toss that crappy death metal you're listening to now out the window and listen to this.
The BeatlesRed Hot Chili PeppersRadioheadMuseColdplayLinkin ParkKanye WestFoo FightersMetallicaNirvana
Angra, Kamelot, Black Sabbath, Mägo de Oz, Freedom Call, Metallica, DJ Mystik, Sonata Arctica, Arch Enemy, Emerson, Lake & Palmer, Rush, King Diamond, Mr. Big, Red Hot Chili Peppers, Blind Guardian, Dethklok, The Click Five, Rhapsody, Stratovarius, Megadeth, Iced Earth, Down, Eternal Tears of Sorrow, Scorpions, Yngwie Malmsteen, Dio, Luca Turilli, Helloween, Dschinghis Khan, Chumbawamba, Nightwish, Bob Marley & The Wailers, Dark Tranquillity, Elvenking, Eyes Of Shiva, Linkin Park, Alice Cooper, System of a Down, Heaven's Guardian, Pain of Salvation, Dark Moor, In Flames, Bee Gees, Labyrinth, Devin Townsend, Rammstein, Amon Amarth, Xandria, Beastie Boys, Avantasia