Where to begin, I listen to a ton of groups that don't get a lot of attention, but should.
The Abbasi Brothers - Mellow post rock with some electronic influences
Aeon Spoke - Side project of Paul Masvidal of Cynic.
Agalloch - Dark Metal from Washington State (if I remember correctly) if you're a fan of opeth you'll definitely love this group
Alcest - French Shoegaze from the musical genius Neige. Souvenirs d'un autre monde is probably one of my favorite albums of all time
The American Dollar - Great post-rock with just enough electronica. Great chillout music.
Amesoeurs - another project of Neige's. More Punk influenced with some Black Metal influence too.
Day Without Dawn - Fantastic blend of metal and catchy riffs and singing. Their LP is way too short, but amazing
Daylight Dies - Great Death/Doom band from America, really clean growls and very depressing Riffs.
The Dear Hunter - Progressive Rock project who just (leaked) their third of six albums. each album is a part of a 6 act play which tells the story of a young man's life from birth to death.
The Depreciation Guild - really catchy shoegaze/chiptune mixup that is really great. Their albums are free for download from their site.
Devil sold his soul - one of the few post-hardcore groups that are actually interesting, worth checking out if you're into that sort of thing.
Do Make Say think - preeminent post rock band from canada. canada churns out some of the best post rock this decade
earshot - great rock band from illinois? the singer sounds a lot like M.J.Keenan from Tool.
Electric Wizard - FUCKING STONER DOOM DUDE
Explosions in the Sky - awesome post rock to fall asleep to. very emotional music.
Giant Squid - awesome sludge band out of somewhere in america. definitely check them out, really great stuff, the singer is amazing
Godspeed You! Black Emperor - Wrote the book on Post rock. also from canada
Gojira - awesome death/grove metal band from france. very deep lyrics, from mars to sirius is one of my favorite metal albums of all time. pretty good album art to boot
Gordian Knot - One of the side projects of Sean Malone of Cynic. very good progressive rock stuff with a lot of guest appearances from various other bands.
Have a Nice Life - amazing shoegaze/doom music ABSOLUTE MUST HAVE
Isis - when you think post-metal, you can't help but think of this group.
Katatonia - Death/Doom band that has progressed to playing more depressive Rock. all of it is top notch though. this is one of those bands in which the fans are always ranting and raving that their older stuff is better.
Massive Attack - Trip hop group that has a great discography. this group got me into appreciating electronic music. Do you like the intro theme to House? well this group does it.
Mogwai - another preeminent Post Rock band, but not as atmospheric as GY!BE.
My Bloody Valentine - Greatest Shoegaze/Dreampop group to grace the face of the planet. Get loveless, crank up the volume and enjoy wall of sound.
November's Doom - Great Death/Doom metal band. if you enjoyed Daylight Dies, you'll definitely love these guys.
The Pains of Being Pure at Heart - just released their ST album. if you enjoy the shoegaze above, then this will not let you down. a bit more pop sounding, but great still.
Pelican - Best post-metal group. period. Isis may be the posterboys, but this is where its at.
A Silver Mt. Zion - great experimental rock group with members of GY!BE. thier first full album is a bit more experimental than 13 blues.
Silversun Pickups - Great shoegaze band. I have not removed their latest album off of repeat since it came out.
The Warlocks - Imagine if Thom Yorke hung out with stoners who worshipped Black Sabbath, and then Thom and those guys formed a band. well this is it.
We made God - Great Icelandic Post Rock/metal group. if you enjoy the Deftones, then this band is really worth checking out.
Wolves in the Throne Room - American Atmospheric Black Metal. the TROO KVLT crowd frowns on this band, but I think this group is one of the best Black Metal groups currently recording/touring.
if you liked that, more to come.