Props for the mention of Gabriel Knight:Sins of the Fathers, but I fear that’s mainly my nostalgia kicking in.
For my part I’ll mention some notable C-64 tunes.
Rob Hubbard’s Commando is awesome.
Martin Galway’s Comic Bakery
Ocean Loaders 2&3. For those blissfully unaware of what a Loader track is, it was the music that played while you waited for the game to load from your cassette deck into the C-64’s internal memory. This usually took 4-5 minutes and the game companies thought we might want to have something to experience during the wait. So they included Loader tracks that played while you waited for the fun to start. Like elevator music, for games.
For those who want to get mp3’s of old C-64 tracks I recommend sid.oth4.com. The site offers up original re-recordings of hundreds of SID-tracks (the music format of the C-64) done through a SID hardware chip sound board to make sure it sounds just like it did when it played on an actual C-64 but even if you’re not quite as big of a music nerd as to demand exact fidelity it’s still an excellent site.