I've been getting into Mogwai and Explosions in the Sky as of late. The album art and vinyl packaging for Take Care, Take Care is outstanding and a must buy.
If there are other groups I should look into, please let me know!
Sigur Rós
Labradford, Jessamine and the whole Kranky scene/label
Tortoise - fathers of the genre
Cul de Sac
Couch
Rachel's
Circle - finnish band whose early works are a pretty unique take on krautrock/post rock, get "Hissi" or "Pori" or "Fraten".
Do Make Say Think
Godspeed you Black Emperor - one of the exponents
Giardini di Mirò
Tristeza
Kinski
Labirinto - brazilian band, if you want something exotic in the genre
These are just some of my faves, there are tons more...
Definitely try Godspeed you Black Emperor!, Rachel's and Mogwai. And the band that Keith used to start the thread, Explosions in the Sky.
Oh, and I forgot another cool band from that period, A Silver Mt. Zion.