For action sequences (and it's almost completly instrumental too) check out Esplendor Geométrico and Sonar.
Sonar:
You can listen to some of their tracks on last.fm, but it's mostly remixes. The originals are a lot better:
Sonar – Listen free and discover music at Last.fm
Here's a track on yt: [ame=http://www.youtube.com/watch?v=KKh77hT8o1k]YouTube - Sonar-Tehoma[/ame]
Esplendor Geométrico:
yt: [ame=http://www.youtube.com/watch?v=Edc15I5oRRo]YouTube - ESPLENDOR GEOMETRICO - MALOS TRATOS[/ame]
[ame=http://www.youtube.com/watch?v=yONfdBnvk54]YouTube - Esplendor Geométrico - El Acero del Partido[/ame]
For slower, more atmospheric sequences I recommend Sunn O))), Electric Wizard, Cheerleade 69 and Esoteric.
Sunn O))):
yt: [ame=http://www.youtube.com/watch?v=sG97k6DMNVM]YouTube - Sunn O))) - Báthory Erzsébet[/ame]
Electric Wizard:
yt: [ame=http://www.youtube.com/watch?v=sO7VP34n2Ps]YouTube - Electric Wizard - Funeralopolis[/ame]
Cheerleader 69:
MySpace.com - Cheerleader 69 - - Ambient - www.myspace.com/cheerleader69theband
Esoteric:
yt: [ame=http://www.youtube.com/watch?v=ANry2j1U4C8]YouTube - Esoteric - Circle[/ame]
As a summary: I think old school industrial and rhythmic noise (as opposed to harsh noise) work well for action passages and I like to use drone ( Sunn O))) ), funeral doom (electric wizard, esoteric) or ambient / apocalyptic folk (Cheerleader 69) for ambience.
Be careful when looking for others apocalyptic folk (and neofolk) bands, because a lot of bands from this genre are racist / white power idiots that imo shouldn't be supported at all. (Thisi s why I only mention Cheerleader 69, because they are clearly not revisionists or similar scum)