I'm not particularly musically inclined. That being said, I love music and games that use music well.
I've experimented with numerous online music composition programs (particularly ones that do a lot of the work for you), and I want to draw you attention today to BeepBox.
It's one of the most robust chiptune music composition programs you'll find that also manages to stay user-friendly and easily approachable.
You can, like me, just start clicking stuff and, as if by magic, it'll probably sound good. Keep layering and adding to it and you'll have a pretty cool song pretty quickly.
If you actually have musical talent, you can change the key, rhythm, scale, as well as various instrument settings, and make a pretty awesome, complex song that sounds like it's straight out of one of the great chiptune albums of yore (like the VVVVVV soundtrack, for example).
All of the song data is stored in the URL, so all you have to do to save it is bookmark the page once your song is created. PRETTY sweet, to say nothing of the remarkably easy .wav export button.
Beyond that, it has built in Twitter functionality. Even if you don't use Twitter, you can take a look at the feed of people sharing their songs, and, if you're not feeling all that confident about your own creations, you can reach out to someone who is and ask for permission to use their songs. I've done this in the past and people have been very willing to share their work (provided I wasn't making money off of them, which I wasn't).
So, give it a try. Share your songs with me on Twitter or in the comments! Here's one I whipped up in a few minutes to get you started.
Quick shout-out to John Nesky for making such an awesome piece of software!