Yeah, what Nev said.
I noticed Winds and Vintersorg were mentioned on this page as avant-garde. I'm not so sure about that. They're both great, either way.
And here's some avant-garde recommendations...
Arcturus
Ulver
Solefald
Sigh
Virus
Ved Buens Ende
Fleurety
Unexpect
Age of Silence
Peccatum
Maudlin of the Well
Kayo Dot
Fantômas
Diabolical Masquerade
Smile Carved Sour
Ram Zet (I'm still not into them yet, but I'm sure some will like them)
Thee Maldoror Kollective (Just get Pilot [Man With the Meat Machine]. I've heard their earlier stuff and it isn't good)
And there are some good bands that may not be considered avant-garde metal, but are still either experimental or sound pretty different...
Farsot (pretty weird black metal)
Blut Aus Nord (same as above)
Negura Bunget (NG won't let me use a certain character that's in the name) (same as above)
Aarni (experimental doom)
Gonin-Ish (weird extreme prog)
Behold...the Arctopus (experimental tech prog)
Mirrorthrone (experimental black/death)
Vindsval/ le Grand Guignol (crazy symphonic black with carnival aesthetic and hysterical laughing and crying)
I'm pretty sure I've left out some stuff, but whatever. One other avant-garde project that might be good (MIGHT be good) is Karaboudjan. I'm going to check it out if I can and see if I like it. There was only one 20 minute EP, so I'll try to get that.
In other news, I've been listening to Dan Swanö. good stuff. Since he does death metal, this makes the 3rd or 4th death metal project I actually like.