Hello,
Katatonia and Riverside were already mentioned in this thread, and can definitely agree. Katatonia has a pretty varied discography, but personally I find The Great Cold Distance and Tonight's Decision to be their best - TGCD sounds quite modern and is probably their heaviest, while TD is more "open" and maybe slightly less consistent, but amazing nonetheless. Another option is Viva Emptiness which is probably their catchiest and most accessible, though Night is The New Day is also excellent (but it's not as dark as their other albums). Riverside, on the other hand, has 4 perfect albums, but if you're looking for dark and atmospheric - totally Rapid Eye Movement. It's their most consistent and has an incredibly thick atmosphere.
In the prog direction, I can also recommend a fairly young Polish band called Votum, especially the second album called Metafiction. It was a great surprise for me and it's really an amazing album. I'd say it has some slight Riverside and maybe Marillion inspiration, but... well anyway, I think it's worth trying the opening song, called Falling Dream, which represents the album fairly well.
https://www.youtube.com/watch?v=Wi2XH1G2x6YFinally, in extreme metal, Moonspell is amazing. There are both growls and clean (though fairly low, baritone) vocals, and their discography is quite varied, but as the starting point I'd recommend the album Antidote.