try looking for something by kenji kawai (he did the soundstrack for ghost in the shell)
to be honest, high budget animes tend to have some of the best atmospheric music ive been able to find, as well as high budget games.
american mcgees alices has some great atmosphere music by chris vrenna of nine inch nails. marilyn manson also has done some interesting music scores for movies and games that are nothing like his normal style and have a dark atmosphere to them.
cowboy bebop has one of the best soundtracks to anything ive heard, and has a sort of rugged space western mixed with blues feel to it, but that could work well in a post apocalyptic style.
(or just anything by the seatbelts or yoko kanno)
lost keys from the newest Tool album is an intro track that has some pretty interesting subtle music playing in the background, and is VERY atmospheric in anture.
go check out "a celebration of the death of man" and its follow up track "and hte great cold death of the earth" by Aggaloch
the band Adagio has some very decent instrumentals that play out pretty well, but they may be too dominant to be considered "atmospheric". maybe with a little bit of very simple editing htey could be softened appropriately.
would a cyber-punk theme work for a post apocalyptic theme to you?
if so check out Alec Empire
i suggest the song "make em bleed". played at a low volume itd be a great background noise.
apocalyptica. all of their stuff.
i mainly suggest "beyond time" and "path"
also, pick up some of the acoustic intro sets by arch enemy, they have a great atmosphere going on, and its nothing too dominant.
"Day 1: Vigil" by Ayreon.
lol, thats mostly just from the "A's" of my collection and a few songs on my current playlist. if you like the suggestions, or needsome help finding hte songs, jsut ask and ill help ya with more. ive got a pretty massive collection of obscure and popular bands and styles of music.
gosh