To recommend music, specify when the music should be played, followed by the "artist - track", and (if you'd like) a link to a sample (youtube is fine). For example...
Dungeon:
Celldweller - http://www.youtube.com/watch?v=cRawUCNnmsM
Celldweller - http://www.youtube.com/watch?v=cRawUCNnmsM
FO3's vanilla soundtrack just doesn't cut it for me anymore. It was adequate for a year and I didn't want to mess with it because I like how the tracks blend into each other seamlessly enough. Buuuuut, I've gotten to the point where I'd rather play in silence.. After listening to internet radio for a while, I found a few instrumentals that I felt would work great in FO3.
So I've set off looking for more thematic (very subjective) music, again instrumentals, with eerie/dark soundscapes. My search brought me to a couple of bands, one I already knew and another I just discovered.
The following are kinda in order of most appropriate (high to low):
Dungeon:
Nine Inch Nails - http://www.youtube.com/watch?v=UJQC4AYQQJc
Nine Inch Nails - http://www.youtube.com/watch?v=T6R8GCX_wSs
Nine Inch Nails - http://www.youtube.com/watch?v=TvtYSJnm7Lc
Nine Inch Nails - http://www.youtube.com/watch?v=A6TBJEDYU2E
Nine Inch Nails - http://www.youtube.com/watch?v=qc5G7r3PUlM
Celldweller - http://www.youtube.com/watch?v=hh9YGLM1O0k
Celldweller - http://www.youtube.com/watch?v=cRawUCNnmsM
Celldweller - http://www.youtube.com/watch?v=TydwdeJhIAI (gets a little heavy toward the end)
Battle:
Celldweller - http://www.youtube.com/watch#!v=KQZAZ20S_PU&feature=related
Nine Inch Nails - http://www.youtube.com/watch#!v=GHkhwmSq9t8&p=B2583D83A6276FCC&index=32
Nine Inch Nails - http://www.youtube.com/watch?v=Opbrn8FNpI4
Nine Inch Nails - http://www.youtube.com/watch#!v=DApuMNoN3ME&feature=related
Nine Inch Nails - http://www.youtube.com/watch?v=M_0cZ658PO0&p=B2583D83A6276FCC&playnext=1&index=25
The Crystal Method - http://www.youtube.com/watch?v=Out4wtHLFBE
Celldweller - http://www.youtube.com/watch?v=hOdA2xi6Luc
Celldweller - http://www.youtube.com/watch?v=lA00LuSev9Q
Celldweller - http://www.youtube.com/watch?v=tO-zvcPyc7E (hard rock/metal-ish)
Celldweller - http://www.youtube.com/watch?v=1wfKqMjJkMk
Nine Inch Nails - http://www.youtube.com/watch?v=-Fs-HKUSkic
Nine Inch Nails - http://www.youtube.com/watch?v=i3xNNleV1aA
Nine Inch Nails - http://www.youtube.com/watch#!v=84bV_2Qvhe4&p=B2583D83A6276FCC&index=31
Nine Inch Nails - http://www.youtube.com/watch?v=wIQTxXeUCa8 (takes a while to get into the heavy battle stuff, try editing)
Quentin Grey/Methadone/Tobias Tinker - http://www.youtube.com/watch?v=6ai0mOcXrZ4 (electronic)
Celldweller - http://www.youtube.com/watch#!v=TQPnZ7x1zQ4&feature=related (heavy electronic)
Celldweller - http://www.youtube.com/watch#!v=TcBKmwFcP_U&feature=related (heavy electronic)
Explore:
Nine Inch Nails - http://www.youtube.com/watch?v=HSZhBParVjo I (even sounds like there's a bomb warning siren)
Nine Inch Nails - http://www.youtube.com/watch#!v=tG4I8FovIAU&p=B2583D83A6276FCC&index=34
Nine Inch Nails - http://www.youtube.com/watch#!v=5XipJzHD4s4&p=B2583D83A6276FCC&index=28
Nine Inch Nails - http://www.youtube.com/watch?v=7Wv2ongb8_c
Nine Inch Nails - http://www.youtube.com/watch?v=srJYQESO34g
Nine Inch Nails - http://www.youtube.com/view_play_list?p=4B62284E89BE4E57&playnext=1&v=oTYb5XwJ7Ss
Celldweller - http://www.youtube.com/watch?v=Qf83qR5j9Gs
Celldweller - http://www.youtube.com/watch#!v=KQRWPcURwFw&feature=related [appropriate for battle music too]
Celldweller - http://www.youtube.com/watch#!v=_lnHHlrIjGc&feature=related [appropriate for battle music too]
There's probably a ton more by the following artists:
Massive Attack
Russian Circles
Celldweller
My apologies for any broken links. Also if there are other categories I missed, please go ahead and list them (indoors maybe?).