Watch the video under "Mars Volta Interview revu.nl (in Amsterdam)"
At around 5:10 Omar says all of their music is basically pop, which it is. To me they are a blend of prog, punk, and pop. Have you heard their previous band, At The Drive In? It's good to know a bit where their coming from. They are pretty structured in terms of most of their songs. Of course intros and stuff make it seem more conceptual.
As far as math rock, the band Hella with Zack Hill on drums could definitely be considered there. I'm not sure if this counts either, but Marnie Stern has an album with Zack Hill called "This Is It and I Am It and You Are It and So Is That and He Is It and She Is It and It Is It and That Is That"
As far as post-rock, I strongly recommend the French band Kwoon. http://www.kwoon-music.com/
Kwoon - I lived on the Moon
Edited by amhso - 5/23/10 at 7:12pm