Iced Earth - Something wicked This Way Comes, especially the ending trilogy of the album.
Zero Hour - Towers of Avarice. They might not be so "epic", but the song concepts are to that direction.
Kamelot - Epica. Guess the name says it all...
You'll love it, try their Karma album too.
Edguy - Vain Glory Opera. Their best album IMO.
Avantasia - Parts 1 & 2. Tobias Sammet's (Edguy) solo project. Many different singers and several guest musicians. Both albums tell the story, so... you know... a metal opera.
Dark Moor - Between Light and Darkness and/or
The Gates of oblivion. I haven't listened them very much. Download a few songs before buying the CD.
Virgin Steele - The House of Atreus pt. 1 & 2,
The Marriage of Heaven and Hell pt. 1 and 2. Worth trying, trust me.
Redemption - Redemption. Jason Rullo's (we ALL know who he is...
) side project. Excellent music, but not very "epic". But still, one of my most prized possessions... Very Well Done.
The a few others worth concidering:
Lost Horizon,
Rhapsody,
Luca Turilli (Rhapsody's guitarist),
Adagio,
Gamma Ray,
Helloween,
Conception (not very "epic" one might say...),
Arjen A. Lucassen's ALL projects, but:
Ayreon (all albums, but you might find
Flight of the Migrator quite interesting),
Star One (Sir Russell Allen is on this album, great album IMO).
Should give you some new bands to look into...
PERSONAL UPDATE: My "metal" list is almost ready for the large crowds... Just a little fine tuning left...