Musically, it's gotta be Virgin Steele. Their last five albums are by a long shot the greatest Epic Power Metal ever made - extremely diverse, deep and complex music, lots of well-used and sincere influences from classical music, some of the (if not THE) best vocals around, genius guitarworks, simply impeccable songwriting and excellent lyrics too. I can think of only ONE album that's on a par with The Marriage of Heaven and Hell Part One or House of Atreus Act II.
I guess the next best thing would be Rage, as they've consistently supplied raw, heavy Power Metal ranging from good to outstanding in quality over the last twenty-one years with no less than 17(!!!) full-length albums, and not a single loser among them. Can't reach the highs of VS though, imo. Still, Black in Mind, Ghosts, Reflections of a Shadow, End of All Days, The Missing Link and many others are all ace albums.
Oh yeah, a must-mention are also Jag Panzer. Ample Destruction is definitely the best 80s Power album, and one of the few abums that at least come close to Virgin Steele's best. A good bit of their later works are winners too, though I've only heard about half of those so far. And they have one of the most impressive vocalists around.
Other notables but not the best imo(at least musically) are Metal Church (their later albums are absolutely awesome Atmospheric PM with some thrash in between, and Hanging in the Balance is the only thing on a par with Virgin Steele), Gamma Ray ( one great album after another ever since Land of the Free came out, and Power Plant just plain rocks - plus Hansen is an amazing vocalist), Blind Guardian (very consistent, quite raw and heavy apart from the last album, unique vocals and very varied in style), Grave Digger (another very consistent and quite heavy band looking back at over twenty years of ownage), Running Wild (ace speed/power with kick-ass powerful vocals) and HammerFall (quite straightforward, but excellent riffing in a very 80s PM vein, cool songwriting and awesome live shows)