My recommendations will have a lot of classic stuff just to get you started. I'm sure once everyone else pitches in, you'll have a fairly interesting list to look forward to, friend.
Black Sabbath: S/T, Paranoid, Master of Reality, Sabotage, Sabbath Bloody Sabbath, Heaven and Hell
Metallica: Kill 'Em All, Ride the Lightning, Master of Puppets, ...And Justice for All
Megadeth: Rust in Peace, Peace Sells...But Who's Buying?
Iron Maiden: S/T, Killers, Powerslave, Somewhere in Time, Piece of Mind
Mercyful Fate: Melissa, Don't Break the Oath
King Diamond: Fatal Portrait, Them, Abigail
Judas Priest: Sad Wings of Destiny, Sin After Sin, Painkiller, Defenders of the Faith, Stained Class
Saxon: Denim & Leather, Wheels of Steel, Strong Arm of the Law, Lionheart
Diamond Head: Lightning to the Nations
Candlemass: Epicus Doomicus Metallicus, Nightfall, Tales of Creation, Ancient Dreams
Cirith Ungol: King of the Dead, Frost and Fire, One Foot in Hell, Paradise Lost
Opeth: Orchid, Morningrise, My Arms Your Hearse, Blackwater Park, Ghost Reveries
Dissection: Storm of the Light's Bane, The Somberlain
Sacramentum: Far Away from the Sun, Finis Malorum
Insomnium: Winter's Gate, Shadows of the Dying Sun
Dark Tranquility: The Gallery, The Mind's I, Damage Done, Fiction, Character
Vinterland: Welcome to My Last Chapter
Katatonia: Dance for December Souls, Brave Murder Day, Discouraged Ones
Edge of Sanity: Purgatory Afterglow, Crimson I&II
At the Gates: The Red in the Sky is Ours
I could add more but I'll stop there to let anyone else put some recommendations in.
