Well since plenty of the albums I'd put here are already... here, I'll post my favorite metal ones. The two I think should be listed...
Blind Guardian -
A Night at the Opera
I must list this because there's only... two or three people here I know of that like them.

Well, the album is simply amazing. It's so heavily orchestrated and the lyrics are rooted in literature and filled with allusions. And the songs kick ass. Every single one. The bonus track is great, too - "Harvest of Sorrow" in English, but my version is Spanish... "Mies Del Dolor" or "Moisson de Peine" in the French recording. I think they also recorded it in Italian. First time I'd heard him sing in a different language and he sings it perfectly. Album name attributed to Queen's
A Night at the Opera, not the semi-famous Marx brothers film. Not quite as heavy as
Imaginations From the Other Side but even more musically inclined than their
Silmarillion tribute to Tolkien,
Nightfall in Middle Earth. Highlight songs: "Sadly Sings Destiny," "The Age of False Innocence," and the amazing 14 minute tribute to Homer's
The Iliad, "And Then There Was Silence." It seems Hansi (the singer) pays tribute to the scops of old. And the drums are more amazing than any drums I've ever heard... but I still like Tool's.

Anyway, this is my favorite album of all time, very possibly.
Symphony X -
The Odyssey
First album of theirs that I'd heard, took a few listenings-to in order to get used to it. At first, they reminded me too much of Pantera with their guitar arrangements until I realized they are much more complex and not nearly as Neanderthalic as Pantera's. Beautiful album in all, ending it with a 24 minute tribute to Odysseus's journey in Homer's
The Odyssey. But then, there is a slightly disappointing bonus track that really should have been placed elsewhere on the CD. Preferably at the beginning. The juxtaposition makes sense, but the album would be better ending with "The Odyssey." Other highlight: "Accolade II."