Hello! Here's my short list - I tried to pick the best album of each artist of my choice, in my opinion.
Arena - The Visitor
Ayreon - The Dream Sequencer
Blind Guardian - Imaginations From The Other Side
Bruce Dickinson - Balls To Picasso
Dark Tranquillity - Projector
Dream Theater - Six Degrees Of Inner Turbulence
Enya - Watermark
Evereve - Stormbirds
The Gathering - Souvenirs
In Flames - Colony
Neal Morse - ?
Paradise Lost - One Second
Theater Of Tragedy - Aégis
Vision Divine - The Perfect Machine
Within Temptation - Mother Earth
Those are pretty much essential, not really in any particular order, but who would know, Arena got 1st place in the list anyways
Yep, I like Enya too. And some other nonsense stuff (like Philip Glass, old Björk stuff, Massive Attack, etc)
And there are a lot more, but depends on my mood (like Nevermore or Tristania when I'm mostly angry and depressed) and time of the year (like Vince Guaraldi's 'A Charlie Brown's Christmas' is a must "leave playing in the house during December" thingy).
Since I should change my list should my taste change, here's what I've been listening to at the moment in this particular order:
Arena - Seventh Degree Of Separation (Recently bought it, and enjoying it quite a lot... while playing Skyrim
The other Arena albums - which I shuffle with SDoS while working
Theatre Of Tragedy - Forever Is The World (driving home from my girlfriend's)
Blind Guardian - A Twist in The Myth (another Skyrim essential soundtrack alongside all Blind's albums)