Kevin MacLeod -
http://incompetech.com/m/c/royalty-free/
Kevin MacLeod already has blanket permissions for FFR, but I'm just reminding you because his music is actually pretty interesting.
CCMixer -
http://ccmixter.org
CCMixer is hopelessly indie and lacks a lot of the strong, driving rhythms which make for good stepfiles. However, there's still interesting material on there and it's usually unlike anything you've heard before. By using the tag feature you can find music to the tastes of the Stepmania/FFR audience, though it takes some digging.
Try these:
http://ccmixter.org/files/donniedrost/26144
http://ccmixter.org/files/qpec/29580
http://ccmixter.org/files/rebelspirit/29890
and this guy in general:
http://ccmixter.org/people/morgantj
I liked this one a lot:
http://ccmixter.org/files/morgantj/26416
Jamendo -
http://www.jamendo.com/en/
Jamendo is a goldmine for creative commons music from international artists. Much of the music I've seen here has been of high quality, and unlike CCMixer is usually step-friendly.
Here's some Jamendo albums I found (usually with the license first, then a description of the music):
http://www.jamendo.com/en/album/72183 - 100% creative commons; RPGesque instrumentals
http://www.jamendo.com/en/album/49570 noncommerical; spanish industrial folk IDM. And it's actually pretty steppable?!
http://www.jamendo.com/en/album/59841 noncommercial; I really liked the title track from this album
http://www.jamendo.com/en/album/21131 noncommercial; tranquil french idm
http://www.jamendo.com/en/album/62009 noncommercial; mexican IDM. very steppable.
http://www.jamendo.com/en/album/3480 all of Celestial Aeon Project's music is noncommercial. very RPG.
http://www.jamendo.com/en/album/57375 noncommercial contemporary classical; I can't tell if this is recorded with actual instruments so I can't tell if you'll have to go through ddream hell or not
http://www.jamendo.com/en/album/36315 very liberal license; very epic; very RPG, short music too
http://www.jamendo.com/en/album/70768 liberal license; orchestral; epic; medieval
http://www.jamendo.com/en/album/35913 liberal license; very epic stepman battle swing your dicks out on floating platforms or something fuck it I'm running out of adjectives just listen to it