Green Carnation - either what Sintheros said, or Blessing in Disguise, which is a great heavy/progressive metal album with basically no weak song. Regardless of what you choose first, you MUST try The Acoustic Verses later, probably the most amazing acoustic album ever recorded.
Katatonia - The Great Cold Distance if you're looking for something darker and heavier as a whole, Night is the New Day if something less depressive and with more much calmer songs. After you've tried the two, the masterpiece which is Viva Emptiness. Then, I guess the earlier albums, I haven't heard them myself yet, but they're definitely less accessible (though all of them are liked, so I guess you can't go wrong).
The Pineapple Thief - Tightly Unwound. Excellent and very accessible at the same time. I don't know anyone who would not love this album at the first listen.
Riverside - if you're into something heavier, Anno Domini High Definition. If something calmer, Out of Myself. Both are excellent in their own direction. Either way, leave Rapid Eye Movement as the last album you'll listen to. It's definitely the most difficult to get into, but... worth it. Entirely.
All I can recommend myself.