I've been getting more into Opeth lately, and I'm looking for some other bands with a similar feel, basically good stuff to chill out to.
Ne Obliviscaris
http://youtu.be/-wa4zqBwPVE
Be'Lakor
http://youtu.be/rYBgWgjjgxQ
Unless you're talking about new Opeth.....
If you're into the "cleaner" part of Opeth:
http://www.youtube.com/ watch?v=9VEFORk1wYA (Soen - Savia)
http://www.youtube.com/ watch?v=ZPSGS-ymseI (Katatonia - My Twin)
Devin Townsend albums Ki and Ghost are really calming.
If you're more into their growling albums, I don't think there is much to top them to be honest. After I have been through my Opeth period I really liked jumping into Strapping Young Lad (although that may be a bit over the top) and more specifically: Devin's Townsend classic work (although his recent work is also very very good).
http://www.youtube.com/ watch?v=n-DKs0qfdEk - Juular
http://www.youtube.com/ watch?v=NaKvwsl2rmw - Deadhead
http://www.youtube.com/ watch?v=UZF3qmGfDws - Earth Day
http://www.youtube.com/ watch?v=Ole-zxwxQno - Stand (It even features Mikael from Opeth! :-) )
http://www.youtube.com/ watch?v=H5BqyluKkk0 - Hyperdrive
Also bands like Gojira are a bit similar, in that they are progressive metal but can be very rough.
http://www.youtube.com/watch?v=Lf7i6UB5vGw
As a long time Opeth fan: I can't believe it's not Opeth!
TWO WORDS: DEVIN TOWNSEND. (Can be a little whacky to get into though the first time. Listen to 'Destruction'.....or was it 'Construction'?) Damn. Just give it a listen!
I think 'Deconstruction' was what you were looking for. I listened to it, and then proceeded to mop my brain off the floor. And yes, that is a good thing.
As good as Devin can be (or more to the point, was..) I'm not sure if any of his music is too similar to Opeth.
Enslaved are to black metal what Opeth are (were) to death metal, using lots of 70's classic and prog rock influence.
http://youtu.be/PNUJ0l32YQw
Check out Leprous. http://www.leprous.net/
Listen to the Deadwing album from Porcupine Tree. Akerfeldt and Wilson are pretty tight. They made Storm Corrosion together.
I find the lack of Ghost in this thread rather disturbing
http://www.youtube.com/watch?v=KCkoIEbjbsM&list=RDdQDaWoWwqdM
Listen to Katatonia. Similar to Opeth's style. They're really good especially with the clean singing parts. You'll love it. Orphaned land are turkish folk metal. I've heard their recent album and it's pretty good. But they aren't similar in style. Opeth has more of a western prog\classic influence. Orphaned Land have their 'Turkey' music influence (for lack of a better word). To be honest though, Katatonia and Opeth are up there along with Devin. :D
No one mentioned Tool
You should definitely listen to their album Lateralus
Btw, some of these bands mentioned above are awesome but they are really mixed up, and not in some order like they are in liferescripted's comment
Katatonia has been mentioned before, but check out their Brave Murder Day album; Mikael does the vocals on that album, it's fucking wonderful.
Aside from that... November's Doom, Novembre's 'Classica' album, some Swallow the Sun...
...it really depends on what era Opeth you'd like most.
http://www.youtube.com/watch?v=7cCkrimLgiw
I think that these guys do Opeth better than Opeth.
if you're looking for stuff to chill out too, check out Alcest. Earlier stuff was black metal, then it got mixed with shoegaze. Which he pretty much start the whole blackgaze thing. I don't like the title, but the music is great.
You may like Riverside
https://www.youtube.com/watch?v=rO_SRMfm7Uo