It's a nice challenge to be limited to three monophonic voices, and it's a wonderful feeling to manipulate the lovely SID chip. A few years ago, I looked into researching music tools and resources for the C64 and stumbled across SIDWizard. I tried a few other older tools and editors, but SIDWizard is very well documented and has a very intuitive interface!
You can listen to some of my SID tunes on this neat webplayer called DeepSID.
Or you can directly download my SID files with a PC SID player here.
Furthermore if you're super geeky like me, you can download this disk image to play on the real thing!
And finally, for convenience, here's a YouTube playlist to watch videos of the tunes in action.