1/ Somewhere Far Beyond (one of the best speed metal records ever IMO)
2/ Imaginations from the Other Side (same as above)
3/ Tales from the Twilight World
4/ Nightfall in Middle Earth
5/ A Night at the Opera
6/ Follow the Blind
7/ Battalions of Fear (good but under-developped at the time)
But you can't go wrong with any BG
As for covers their rendition of "Trial by Fire" is awesome!
And on the "Forgotten Tales" compilation I'd like to mention the acoustic version of "Lord of the Rings" which is better than the original IMO.