I really have many, many favorite bands so it's hard for me to say just one, so I have a few.
Anathema - beautiful music that can't be matched by anybody.
Enslaved - Amazing, powerful ideas that always come together - they're creative and are always progressing.
Arcturus - beatiful and strong in every aspect. They haven't released a song I dislike, they are all very talented, and they reach me in a way that no other band can do.
Neurosis - They're unique, they have a whole different atmoshpere than other bands, intensely emotional, and are always progressing.
Opeth - amazing ideas and have never failed to inspire me.
Cryptopsy - no death metal band has ever done what they do for me. They are unique, have great ideas, and never fail to pull it all together as a band.
Katatonia - great band. The most simple ideas are the most amazing and inspiring.
Those are a few. There are so many other bands that should be listed that aren't, or that are barely below it.