I've been getting at the files of various games (musical or not) and trying to rip their music for a long time now. It might've been the reason I got into GH modding in the first place! Since then, I've been trying to put together boxsets of game soundtracks for as many games as I care to—which is quite a few.

These are all directly ripped from the game files and mixed to lossless if need be. No recording the game audio, no transcodes, as clean as I can get it. Since a lot of especially full-band rhythm games store their music in Vorbis or MP3, keeping things as lossless as I can is especially important. These are then lightly mastered (no compression, just keeping silence between tracks controlled), sorted into discs, packed up with a readme, and uploaded for your listening pleasure.

I used to upload these to this site directly, but I'm less keen on doing that now for potentially upsetting my web host. Instead, they're now hosted on the Internet Archive, which will let you stream the songs individually and grab them in VBR MP3 or FLAC.

Finished rips

Soundtracks to do/in progress

Karaoke Revolution Volume 3
Soon! While the Volume editions of Karaoke Revolution all use a bizarro early VGS format our tools can't read, the Xbox versions of Karaoke Revolution and Party have all the songs from these games in their files as on-disc DLC—in ADPCM for the former and MOGG for the latter. These aren't encrypted or scrambled and can just be opened in Audacity (provided you have the ffmpeg libraries). The Volume 1 and 2 sets use these versions of the songs as a result.
Karaoke Revolution Party
Also soon! Party, on the other hand, is extremely GH1-like in its file formats, including VGSes. It's completely trivial to mix them down.
Rock Band 2/3/Lego/etc.
Nothing concrete, but likely given a few years. These games all used masters for their songs, so there's less incentive to do mixdowns. Still, I love RB2's soundtrack, and they're all pretty solid and I can get first-gen audio rips for all of them, so maybe.
Guitar Hero III/Aerosmith
Eh, maybe. III used some soundalikes, as did Aerosmith, but I don't know of a tool that can rip them from the game files at current, and that's my big requirement. (I'd rather not use the PC version's 128kbps MP3s as a source.)
Guitar Hero: World Tour/5/etc.
Very distant maybe. World Tour and onwards used all master recordings like the later Rock Band games, and I have basically no nostalgia for them, so likely not. But hey, anything's possible.