your lucky this is the first time i've been on here in awhile, so i guess i'll help you out
post-rock: (in order of how good they are)
explosions in the sky
pelican
godspeed! you black emperor
moving mountains (post rock-ish)
math rock:
uh, i don't really know what math rock is anymore, but i guess horse the band falls into that category. try sky eats airplane too
experimental:
again, experimental is really hard to categorize, but all you really need to know that is legit experimental is frank zappa. and i guess an albatross too, although they're extremely different than frank zappa.
indie:
again, so much gets clumped into "indie" now that it trying to suggest bands is just a joke since it's all subjective and i'm pretty sure none of these bands are on independent labels, but...
neutral milk hotel
modest mouse
death cab
built to spill
camper von beehtoven
dinosaur jr
manchester orchestra
kevin devine
iron & wine