Must listens:
Delain, Epica, Lacuna Coil, Kamelot (skip first 2 albums)
Tons more:
The Gathering (mostly the Anneke years), Sirenia, Xandria, Leaves' Eyes, Stream of Passion, Therion (1996 and beyond), The Dark Element, Diabulus in Musica, Eleine, Ex Libris, VUUR, The Gentle Storm, Ad Infinitum, Tarja (original Nightwish singer does her own solo stuff now)
Probably a bunch of others I can't think of right now